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Solving issues yourself

Got a crash? You can try to find the cause yourself. Just press "Open Logs" button in error window or enable "Logger" in the launcher settings.
Following is a list of relatively simple to detect and common game launch issues, including issues with mods.
All examples below are based on real support requests from our users.

How to find the right section

Find the line with the error in the log - it usually starts with Caused by or contains the words Exception or Error. Then search for the key part of this line on this page (Ctrl+F, or Cmd+F on macOS): all examples below contain real lines from logs

Java and system​

Wrong Java version​

Every game version needs its own Java version. If "Recommended" Java is selected in the launcher settings, the launcher picks it itself. Most often a mod that needs a newer Java than the recommended one is simply built for a newer game version - in this case you need the version of the mod for your game version, not another Java.

Mod requires a newer Java​

Detected by java.lang.UnsupportedClassVersionError in caused by string.

Log example
> Exception in thread "main" java.util.ServiceConfigurationError: net.minecraftforge.forgespi.language.IModLanguageProvider: Unable to load thedarkcolour.kotlinforforge.KotlinLanguageProvider
>   at java.base/java.util.ServiceLoader.fail(ServiceLoader.java:586)
> Caused by: java.lang.UnsupportedClassVersionError: thedarkcolour/kotlinforforge/KotlinLanguageProvider has been compiled by a more recent version of the Java Runtime (class file version 65.0), this version of the Java Runtime only recognizes class file versions up to 61.0
>   at java.base/java.lang.ClassLoader.defineClass1(Native Method)

In this example, it is clear that the mod kotlinforforge failed to load because it is being run on an outdated version of Java. The required Java version can be determined by the class file version, using this website. In this example, the game was launched with Java 17 (61.0), but the mod requires Java 21 (65.0).

What to do:

  • If "Recommended" Java is selected in the launcher settings, the mod is made for a different game version. Download the version of the mod for your game version
  • If Java was selected manually, select "Recommended"

Fabric reports an unsuitable Java the same way as a missing dependency - as a "mod" called java:

Log example
> net.fabricmc.loader.impl.FormattedException: Some of your mods are incompatible with the game or each other!
> A potential solution has been determined, this may resolve your problem:
>    - Replace 'Java HotSpot(TM) 64-Bit Server VM' (java) 8 with version 21 or later.
> More details:
>    - Mod 'Fabric API' (fabric-api) 0.119.4+1.21.4 requires version 21 or later of 'Java HotSpot(TM) 64-Bit Server VM' (java), but only the wrong version is present: 8!

There is no need to find and install the required Java yourself - do the same as described above.

Game requires a newer Java​

Log example
> Error: LinkageError occurred while loading main class net.minecraft.client.main.Main
>   java.lang.UnsupportedClassVersionError: net/minecraft/client/main/Main has been compiled by a more recent version of the Java Runtime (class file version 65.0), this version of the Java Runtime only recognizes class file versions up to 61.0

The same UnsupportedClassVersionError error occurs when the game itself is launched on a too old Java.
Select "Recommended" Java in the launcher settings. If it is already selected, use the "Force update" checkbox.

On NeoForge the same problem may look different - the game crashes before loading mods:

Log example
> Error occurred during initialization of boot layer
> java.lang.module.FindException: Error reading module: D:\Minecraft\game\libraries\cpw\mods\bootstraplauncher\2.0.2\bootstraplauncher-2.0.2.jar
> Caused by: java.lang.module.InvalidModuleDescriptorException: Unsupported major.minor version 65.0

The solution is the same - select "Recommended" Java. If it is already selected, one of the mods is made for a different game version.

Old game version on a newer Java​

Forge, OptiFine and LiteLoader for versions up to 1.12.2, as well as the oldest game versions, use the so-called launchwrapper, which does not work with Java 9 or newer. Such versions will crash with the following log when launched on newer Java versions:

Log example
> Exception in thread "main" java.lang.ClassCastException: class jdk.internal.loader.ClassLoaders$AppClassLoader cannot be cast to class java.net.URLClassLoader (jdk.internal.loader.ClassLoaders$AppClassLoader and java.net.URLClassLoader are in module java.base of loader 'bootstrap')
>   at net.minecraft.launchwrapper.Launch.<init>(Launch.java:33)
>   at net.minecraft.launchwrapper.Launch.main(Launch.java:27)

The solution is to run the game using Java 8. This error almost always means that Java was selected manually - select "Recommended" Java.

Mod requires an older Java​

The opposite also happens - a mod requires an older Java. For example, some mods for 1.16.5 were written for Java 8 and do not work on Java 16. By default, the launcher runs 1.16.5 on Java 16 instead of Java 8 recommended by Mojang, because many mods for this version require a newer Java:

Log example
> [20:43:54] [Render thread/FATAL] [ne.mi.fm.ModLoader/]: Encountered non-modloading exceptions!
> java.util.concurrent.CompletionException: java.lang.RuntimeException
>   Suppressed: java.lang.ExceptionInInitializerError
>   Caused by: java.lang.RuntimeException: Can't retrieve field modifiers from class class java.lang.reflect.Field
>     at ru.timeconqueror.timecore.api.reflection.ReflectionHelper.findField(ReflectionHelper.java:117) ~[timecore:1.16.5-3.4.1.0.build45] {re:classloading}
>   Caused by: java.lang.NoSuchFieldException: modifiers
>     at java.lang.Class.getDeclaredField(Class.java:2549) ~[?:?] {}
>     at ru.timeconqueror.timecore.api.reflection.ReflectionHelper.findField(ReflectionHelper.java:114) ~[timecore:1.16.5-3.4.1.0.build45] {re:classloading}

The key line is NoSuchFieldException: modifiers. In this example, the problem is in the timecore mod. Select Java 8 for this version manually (how to do it).

Java VM Crash​

Sometimes it's not the game that crashes, but the Java Virtual Machine itself:

Log example
[:] #
[:] # A fatal error has been detected by the Java Runtime Environment:
[:] #
[:] #  EXCEPTION_ACCESS_VIOLATION (0xc0000005) at pc=0x00007ff91b3cfdf8, pid=17192, tid=27840
[:] #
[:] # JRE version: OpenJDK Runtime Environment Microsoft-22300 (16.0.1+9) (build 16.0.1+9)
[:] # Java VM: OpenJDK 64-Bit Server VM Microsoft-22300 (16.0.1+9, mixed mode, tiered, compressed oops, compressed class ptrs, g1 gc, windows-amd64)
[:] # Problematic frame:
[:] # V  [jvm.dll+0x69fdf8]
[:] #
[:] # No core dump will be written. Minidumps are not enabled by default on client versions of Windows
[:] #
[:] # If you would like to submit a bug report, please visit:
[:] #   https://github.com/microsoft/openjdk/issues
[:] #

In such logs, there are two key points: the error (in the example above, it's EXCEPTION_ACCESS_VIOLATION) and the library where the error occurred (jvm.dll). Typical solutions involve tracking down which component the error is related to and removing it (if it's third-party software, such as SafeIP), or updating/rolling back (if it's Java or a graphics driver).

The library name tells what it belongs to:

Library name starts withWhat it isWhat to do
nvoglv, nvwgf, nvd3dNVIDIA graphics driverUpdate or roll back the driver
ig4icd, ig7icd, ig8icd, ig9icd, ig11icd, ig12icd, ig75icd, igxelpicd, igvk, igdumd, igd10Intel graphics driverUpdate or roll back the driver
atio, aticfx, amdvlk, amdxcAMD graphics driverUpdate or roll back the driver
jvm.dll, libjvmJavaInstall another Java distribution
SafeIPsSafeIPUninstall the program
LavasoftTcpServiceLavasoft Web CompanionUninstall the program
graphics-hookOBS game captureDisable the "Game Capture" source in OBS or use "Window Capture" instead
medal-hookMedalClose Medal or disable game recording in it
EXCEPTION_ILLEGAL_INSTRUCTION

The EXCEPTION_ILLEGAL_INSTRUCTION error means that the program requires a newer processor than the one installed in your PC. The error may be not only in the graphics driver, but also in a Java or mod library. Try an older version of that program (driver, Java or mod)

Unfortunately, these errors are often non-trivial to fix, and even we might not be able to help. Try Googling, or contact the support of the component's manufacturer (e.g., the graphics driver).

danger

Never attempt to manually delete or replace the problematic dll file! You could make the problem worse or break your OS!

tip

You can try to resolve this issue using this guide

Exit code 1114​

The game closes right after the Backend library: LWJGL version ... line, and the launcher reports exit code 1114:

Log example
> [19:21:07] [Render thread/INFO]: Backend library: LWJGL version 3.3.3+5
19:21:28,697 [MinecraftLauncher] Launcher has stopped.
19:21:28,697 [MinecraftLauncher] Child process closed with exit code: 1114 (0x45a)

Code 1114 means that the graphics driver failed to start. This most often happens on laptops with two graphics cards - integrated Intel and discrete AMD.
The solution is to switch the Windows power plan to maximum performance. Reinstalling the driver is usually not necessary

Out of memory​

The game may run out of either the memory allocated to it or the memory of the whole system. These cases have different solutions.

Not enough allocated memory​

If the game ran out of allocated memory, the log will contain the java.lang.OutOfMemoryError: Java heap space or java.lang.OutOfMemoryError: GC overhead limit exceeded error:

Log example
> Description: Initializing game
> 
> java.lang.OutOfMemoryError: Java heap space
>   at java.desktop/java.awt.image.DataBufferInt.<init>(Unknown Source)
>   at java.desktop/java.awt.image.Raster.createPackedRaster(Unknown Source)

Allocate more memory to the game in the launcher settings (the "Memory (RAM)" option), but not more than is free in the system. Recommended values are listed in the system requirements. If the system has little memory, remove some mods or shaders

Not enough system memory​

If the system ran out of memory, the errors look different:

Java could not reserve the allocated memory
> Error occurred during initialization of VM
> Could not reserve enough space for 1048576KB object heap
Not enough memory or paging file (Windows)
> OpenJDK 64-Bit Server VM warning: INFO: os::commit_memory(0x0000000781000000, 427819008, 0) failed; error='The paging file is too small for this operation to complete' (DOS error/errno=1455)
> #
> # There is insufficient memory for the Java Runtime Environment to continue.
> # Native memory allocation (mmap) failed to map 427819008 bytes. Error detail: G1 virtual space
The system terminated the game due to lack of memory (macOS, Linux)
08:35:36,152 [MinecraftLauncher] Child process closed with exit code: 137 (0x89)

In these cases allocating more memory to the game will not help. What to do:

  1. Check the amount of allocated RAM in the launcher settings: it must be less than the free memory in the system. Allocating less than 1 GiB makes no sense
  2. Close other programs
  3. Restart your computer - this frees memory and reduces its fragmentation
  4. On Windows, check the paging file: press Win+R, type sysdm.cpl, go to the "Advanced" tab - "Performance" - "Settings" - "Advanced" - "Virtual memory" - "Change" and enable "Automatically manage paging file size for all drives"
32-bit Java

On 32-bit Java it is impossible to allocate more than 1 GiB of RAM to the game

Main class not found​

Log example
> Error: Could not find or load main class cpw.mods.bootstraplauncher.BootstrapLauncher
> Caused by: java.lang.ClassNotFoundException: cpw.mods.bootstraplauncher.BootstrapLauncher

If main class is followed by a class of the game itself or of a mod loader (net.minecraft..., cpw.mods..., net.minecraftforge..., net.fabricmc...), the version files are missing or corrupted. Reinstall the version using the "Force update" checkbox. If the error repeats, check your antivirus

Log example
> Error: Could not find or load main class C:\Program Files\Java\jdk-17
> Caused by: java.lang.ClassNotFoundException: C:\Program Files\Java\jdk-17

If something unrelated is there instead - a path, a link or just a word - the "Java arguments" field in the launcher settings contains something extra, and Java took it for a class name. Clear the "Java arguments" field

System language settings​

With some system languages (e.g. Turkish or Arabic) the game and mods put foreign characters into names and then refuse to accept them themselves:

Log example
> net.minecraft.util.ResourceLocationException: Non [a-z0-9/._-] character in path of location: minecraft:dynamic/light_map_١
>   at net.minecraft.util.ResourceLocation.<init>(ResourceLocation.java:33) ~[?:?] {re:classloading}
Log example
> [19:28:11] [Server thread/ERROR] [ne.mi.ev.EventBus/EVENTBUS]: Exception caught during firing event: 'addition' is not a valid enum constant! Valid values are: 'addıtıon', 'multıply_base', 'multıply_total'

In the first example the digit 1 is replaced with the Arabic digit ١, in the second the Latin i is replaced with the Turkish ı. The mods are not to blame here. Add the -Duser.language=en argument to the "Java arguments" field in the launcher settings or switch the system language to English

Non-Latin Windows user name​

Some mods and libraries extract their files to the temporary folder, which is located in the Windows user folder. If the user name is not written in Latin letters (e.g. in Cyrillic), Java may fail to load such a file:

Log example
> Exception in thread "main" java.lang.UnsatisfiedLinkError: Could not load library. Reasons: [no jansi in java.library.path, C:\Users\Пользователь\AppData\Local\Temp\jansi-64-7040785544641368972.dll: Can't find dependent libraries]
>   at org.fusesource.hawtjni.runtime.Library.doLoad(Library.java:182)

Reinstalling the game to another folder will not help: the problem is the user folder, not the game folder. What to do:

  • Set a folder with a Latin path for temporary files: press Win+R, type sysdm.cpl, go to the "Advanced" tab - "Environment Variables" and change the TEMP and TMP user variables to a path of Latin letters (e.g. C:\Temp; create the folder beforehand)
  • A more reliable way is to create a Windows user with a Latin name

GLFW Input Devices Issue​

Some input devices, such as gamepads, joysticks and steering wheels may cause crashes.

Log example
> [14:49:52] [main/INFO] [STDERR/]: [org.lwjgl.glfw.GLFWErrorCallback$1:invoke:105]:    Description : Invalid axis in gamepad mapping 03000000790000000600000000000000 (G-Shark GS-GP702)
> [14:49:52] [main/INFO] [STDERR/]: [org.lwjgl.glfw.GLFWErrorCallback$1:invoke:106]:    Stacktrace  :
> [14:49:52] [main/INFO] [STDERR/]: [org.lwjgl.glfw.GLFWErrorCallback$1:invoke:110]: org.lwjgl.glfw.GLFW.glfwInit(GLFW.java:830)
> [14:49:52] [main/INFO] [STDERR/]: [org.lwjgl.glfw.GLFWErrorCallback$1:invoke:110]: net.minecraftforge.fml.loading.progress.ClientVisualization.initWindow(ClientVisualization.java:58)
> [14:49:52] [main/INFO] [STDERR/]: [org.lwjgl.glfw.GLFWErrorCallback$1:invoke:110]: net.minecraftforge.fml.loading.progress.ClientVisualization.start(ClientVisualization.java:335)

"Invalid axis in gamepad mapping" may indicate a gamepad issue. Disconnecting gamepads (joysticks, steering wheels) will fix it.

OptiFine and rendering mods​

OptiFine - incompatible loader or game version​

OptiFine is a rather finicky mod that requires specific Forge versions.

Log example
> [11:43:13] [main/ERROR] [cp.mo.mo.TransformationServiceDecorator/MODLAUNCHER]: Service failed to load OptiFine
> cpw.mods.modlauncher.api.IncompatibleEnvironmentException: Error loading OptiFine ZIP file: union:/C:/Users/User/AppData/Roaming/.tlauncher/legacy/Minecraft/game/mods/OptiFine_1.21.1_HD_U_J1.jar%23159!/
>   at optifine.OptiFineTransformationService.onLoad(OptiFineTransformationService.java:122) ~[?:?] {}
> [11:43:13] [main/ERROR] [cp.mo.mo.TransformationServicesHandler/MODLAUNCHER]: Found 1 services that failed to load : [OptiFine]
> Exception in thread "main" cpw.mods.modlauncher.InvalidLauncherSetupException: Invalid Services found OptiFine

From the lines services that failed to load: [OptiFine] and Invalid Services found OptiFine, we can see that OptiFine cannot work in the current setup. Most often there is one of two reasons:

  • OptiFine is launched on NeoForge - OptiFine does not work with NeoForge in any version. Remove OptiFine
  • OptiFine is made for a different game version - check the version in the file name (e.g. OptiFine_1.20.1_HD_U_I6.jar will not work on 1.21.1). Install a matching OptiFine version or remove it

OptiFine - incompatible Minecraft version​

OptiFine is tightly bound to a specific game version. While many mods can survive minor updates (for example, mods for 1.19.1 may still work on 1.19.2), this doesn't apply to OptiFine. If OptiFine detects an incompatible game version, the following lines will appear in the log:

Log example
> [21:18:40] [main/INFO] [STDERR]: [optifine.OptiFineClassTransformer:getOptiFineResourcePatched:223]: optifine.xdelta.PatchException: truncated source file, aborting
> [21:18:40] [main/INFO] [STDERR]: [optifine.OptiFineClassTransformer:getOptiFineResourcePatched:223]:  at optifine.xdelta.GDiffPatcher.copy(GDiffPatcher.java:181)
> [21:18:40] [main/INFO] [STDERR]: [optifine.OptiFineClassTransformer:getOptiFineResourcePatched:223]:  at optifine.xdelta.GDiffPatcher.runPatch(GDiffPatcher.java:130)
> [21:18:40] [main/INFO] [STDERR]: [optifine.OptiFineClassTransformer:getOptiFineResourcePatched:223]:  at optifine.xdelta.GDiffPatcher.<init>(GDiffPatcher.java:67)
> [21:18:40] [main/INFO] [STDERR]: [optifine.OptiFineClassTransformer:getOptiFineResourcePatched:223]:  at optifine.xdelta.GDiffPatcher.<init>(GDiffPatcher.java:63)

The key line here is optifine.xdelta.PatchException. If you see this in the log, check that the OptiFine version matches your game and Forge versions.

OptiFine and VulkanMod - conflicts with other mods​

OptiFine replaces game classes with its own copies, so many mods do not work with it.

Error in another mod​

The error often occurs not in OptiFine itself, but in another mod:

Log example
> Caused by: java.lang.NoSuchMethodError: 'net.minecraft.resources.ResourceLocation net.minecraft.resources.ResourceLocation.fromNamespaceAndPath(java.lang.String, java.lang.String)'
>   at com.skniro.skniro_furniture.block.renderer.OvenBlockEntityRenderer.<clinit>(OvenBlockEntityRenderer.java:24) ~[SkniroFurniture-1.5.0-1.20.1-Forge.jar%23159!/:1.5.0-1.20.1-Forge] {re:classloading}

Here the SkniroFurniture mod crashes: it calls a game method (net.minecraft...) that is missing from the class copy modified by OptiFine. If OptiFine is installed and another mod crashes with NoSuchMethodError on a game method, OptiFine is most likely the culprit. Remove it

Dynamic Lights​

Another common example is OptiFine together with the Dynamic Lights mod on 1.12.2:

Log example
> [15:44:50] [Client thread/INFO] [STDERR]: [net.optifine.reflect.ReflectorMethod:getTargetMethod:97]: java.lang.VerifyError: Inconsistent stackmap frames at branch target 47
> Exception Details:
>   Location:
>     net/minecraft/world/World.func_175638_a(Lnet/minecraft/util/math/BlockPos;Lnet/minecraft/world/EnumSkyBlock;)I @32: goto
>   Reason:
>     Current frame's stack size doesn't match stackmap.

Removing OptiFine or updating Dynamic Lights usually helps. OptiFine has its own dynamic lighting (the Dynamic Lights option in the video settings), so the separate mod is not needed with it

Sodium and VulkanMod​

OptiFine is also incompatible with Sodium and mods based on it (Embeddium, Rubidium, Oculus and similar). See Removing OptiFine for details

VulkanMod

VulkanMod deeply modifies the rendering engine and is incompatible with a huge number of mods. In case of a crash, check whether the game starts without VulkanMod

Mods​

Mods for another loader​

Mods for Fabric/Quilt and Forge/NeoForge are not compatible with each other. Most often the loader silently skips a foreign mod, and the game crashes later - for example, because of a "missing" mod. Sometimes the loader refuses to start right away.

Exceptions
  • Quilt runs Fabric mods, but Fabric does not run Quilt mods
  • NeoForge runs Forge mods only on 1.20.1
  • The Sinytra Connector mod allows running Fabric mods on Forge and NeoForge

How to check​

After a crash, the launcher writes the list of mods from the mods folder to the log, together with the loader each mod is made for:

Log example
[:] D:\Minecraft\game\mods
├ aaa-particles-fabric-1.20.1-1.4.12.jar [4952 KiB]
│ ├ md5 = 490f45c52192f63371599f4a07d27908
│ └ aaa_particles [Fabric mod]
│   ├ version = "1.20.1-1.4.12"

The [Fabric mod], [Forge mod] and [NeoForge mod] labels must match the running loader.

  • If there are a few foreign mods, replace them with versions for your loader or remove them
  • If almost all mods are foreign, the modpack is made for another loader. Select a version with the right loader in the launcher

Intentional crash​

Some mods intentionally crash the game when launched on the wrong loader:

Log example
> Caused by: java.lang.UnsupportedOperationException:
> ######################## - USER ERROR - ######################
> User Attempting to load JourneyMap for Forge in Fabric Loader.
> Please Download the Fabric version of JourneyMap.

Missing metadata​

Mods for another loader may lack the metadata the loader needs - then the loader crashes at the very beginning of mod loading:

Log example
> Exception in thread "main" net.minecraftforge.forgespi.locating.ModFileLoadingException: Mod candidate despawntweaks-fabric-1.0.0-1.20.1.jar contains a corrupt or misconfigured toml.
>   at MC-BOOTSTRAP/fmlloader@1.20.1-47.4.21/net.minecraftforge.fml.loading.moddiscovery.ModFileParser.modsTomlParser(ModFileParser.java:52)

Here a Fabric mod (despawntweaks-fabric) is launched on Forge

Extra files in the mods folder​

Mod loaders read only mod jar files located directly in the mods folder. You can see what this folder contains in the mod list the launcher writes to the log after a crash (see Mods for another loader).

Subfolders​

Mods from subfolders (marked as [dir] in the list) are not loaded:

Log example
├ assets [dir]
│ ├ appleskin-fabric-mc1.21.11-3.0.8.jar [175 KiB]
│ │ ├ md5 = e725606e8b0ae1c83ade7cfd0aea9e73
│ │ └ appleskin [Fabric mod]

Here the appleskin mod is located in the mods/assets folder and will not be loaded. Move it to the mods folder itself. The exception is the mods/<game version> folder (e.g. mods/1.12.2), which worked up to 1.12.2 inclusive. Service folders created by mods themselves (e.g. .connector or .index) should be left alone

Extracted mods​

Do not extract a mod jar file unless the mod's installation instructions explicitly say so. Many loaders intentionally crash the game when they see an extracted mod:

Log example
> [11:14:04] [main/FATAL]: There appear to be jars extracted into the mods directory. This is VERY BAD and will almost NEVER WORK WELL
> [11:14:04] [main/FATAL]: You should place original jars only in the mods directory. NEVER extract them to the mods directory.
> [11:14:04] [main/FATAL]: The directories below appear to be extracted jar files. Fix this before you continue.
> [11:14:04] [main/FATAL]: Directory Keystrokes-8.1.2 (1.8.9) contains [MANIFEST.MF]

Delete the folder with the extracted mod and download the mod again (more details)

Installers​

Do not put mod loader installers or the loaders themselves into the mods folder (fabric-installer, fabric-loader, forge-...-installer and similar), as well as mod installers (e.g. Iris Installer). An installer must be run, not copied to mods - see the installation guides for Forge, NeoForge, Fabric and Quilt:

Log example
> [17:59:26] [ForkJoinPool.commonPool-worker-9/WARN] [ne.ne.fm.lo.mo.ModDiscoverer/SCAN]: Skipping jar. File mods/Iris-Installer-3.3.0.jar is a Fabric mod and cannot be loaded

Files that are not mods​

Shortcuts (.lnk), archives with mods inside (.rar, .7z, more details) and Bedrock Edition add-ons (.mcaddon, .mcpack) are not mods. Legacy Launcher does not support Bedrock Edition

Forge/NeoForge - mod error​

If the game crashes because of an error in one of the mods, the culprit can usually be found from the crash text. Below are three ways to do it.

The Caused by line​

There should be a crash at the end of the log. It looks like a series of lines starting with at:

Log example
> Exception in thread "main" [00:23:02] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:1069]: java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
> [00:23:02] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:1069]:     at cpw.mods.modlauncher.LaunchServiceHandlerDecorator.launch(LaunchServiceHandlerDecorator.java:39)
> [00:23:02] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:1078]:     ... 4 more
> [00:23:02] [main/INFO] [STDERR/]: [java.lang.Throwable:printStackTrace:659]: Caused by: org.spongepowered.asm.mixin.transformer.throwables.MixinTransformerError: An unexpected critical error was encountered
> [00:23:02] [main/INFO] [STDERR/]: [java.lang.Throwable:printStackTrace:659]:  at org.spongepowered.asm.mixin.transformer.MixinProcessor.applyMixins(MixinProcessor.java:392)
> [00:23:02] [main/INFO] [STDERR/]: [java.lang.Throwable:printStackTrace:659]:  at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClass(MixinTransformer.java:250)
> [00:23:02] [main/INFO] [STDERR/]: [java.lang.Throwable:printStackTrace:659]:  at org.spongepowered.asm.service.modlauncher.MixinTransformationHandler.processClass(MixinTransformationHandler.java:131)
> [00:23:02] [main/INFO] [STDERR/]: [java.lang.Throwable:printStackTrace:659]:  ... 10 more
> [00:23:02] [main/INFO] [STDERR/]: [java.lang.Throwable:printStackTrace:682]: Caused by: org.spongepowered.asm.mixin.injection.throwables.InjectionError: Critical injection failure: Redirector redirectGetFancyWeather()Z in magnesium.mixins.json:features.options.MixinWorldRenderer failed injection check, (0/1) succeeded. Scanned 1 target(s). Using refmap magnesium.refmap.json
> [00:23:02] [main/INFO] [STDERR/]: [java.lang.Throwable:printStackTrace:682]:  at org.spongepowered.asm.mixin.injection.struct.InjectionInfo.postInject(InjectionInfo.java:468)
> [00:23:02] [main/INFO] [STDERR/]: [java.lang.Throwable:printStackTrace:682]:  at org.spongepowered.asm.mixin.transformer.MixinTargetContext.applyInjections(MixinTargetContext.java:1362)
> [00:23:02] [main/INFO] [STDERR/]: [java.lang.Throwable:printStackTrace:682]:  ... 25 more

Look at the line starting with Caused by: we can see that the problem is with the magnesium mod: Critical injection failure: Redirector redirectGetFancyWeather()Z in magnesium.mixins.json:features.options.MixinWorldRenderer failed injection check.
The culprit is the mod that owns the *.mixins.json file from this line (here it is magnesium.mixins.json). Most likely, it is made for a different game version - install the version of the mod for your game version or remove it.
If one mod extends another (e.g. Iris and Sodium, an addon and its base mod), their versions must match each other - update them together.

The at lines​

Sometimes the problematic mod will appear not in the Caused by line itself, but in one of the at lines below:

Log example
[:] java.lang.RuntimeException: null
[:]     at net.minecraftforge.registries.GameData.postRegisterEvents(GameData.java:320) ~[forge-1.20.2-48.1.0-universal.jar%23185!/:?] {re:classloading}
[:]     Suppressed: net.minecraftforge.fml.ModLoadingException: Age of Weapons - Reforged (ageofweapons) encountered an error during the common_setup event phase
[:] §7java.lang.NoClassDefFoundError: net/minecraftforge/network/PlayMessages$SpawnEntity
[:]         at net.minecraftforge.fml.javafmlmod.FMLModContainer.acceptEvent(FMLModContainer.java:118) ~[javafmllanguage-1.20.2-48.1.0.jar%23182!/:?] {}
[:]     Caused by: java.lang.NoClassDefFoundError: net/minecraftforge/network/PlayMessages$SpawnEntity
[:]         at xxrexraptorxx.ageofweapons.registry.ModEntities.lambda$static$1(ModEntities.java:25) ~[ageofweapons-reforged-1.20.x-v.1.3.2.jar%23166!/:1.3.2] {re:classloading}
[:]         at net.minecraftforge.registries.DeferredRegister$EventDispatcher.lambda$handleEvent$0(DeferredRegister.java:366) ~[forge-1.20.2-48.1.0-universal.jar%23185!/:?] {re:classloading,pl:eventbus:A}
[:]     Caused by: java.lang.ClassNotFoundException: net.minecraftforge.network.PlayMessages$SpawnEntity
[:]         at net.minecraftforge.securemodules.SecureModuleClassLoader.loadClass(SecureModuleClassLoader.java:397) ~[securemodules-2.2.3.jar:?] {}
[:]         at java.lang.ClassLoader.loadClass(ClassLoader.java:525) ~[?:?] {}
[:]         at xxrexraptorxx.ageofweapons.registry.ModEntities.lambda$static$1(ModEntities.java:25) ~[ageofweapons-reforged-1.20.x-v.1.3.2.jar%23166!/:1.3.2] {re:classloading}
[:]         at net.minecraftforge.registries.DeferredRegister$EventDispatcher.lambda$handleEvent$0(DeferredRegister.java:366) ~[forge-1.20.2-48.1.0-universal.jar%23185!/:?] {re:classloading,pl:eventbus:A}

In this example, the error occurs in the ageofweapons mod, which probably doesn't support the Forge version in use - it can't find (ClassNotFoundException) the Minecraft Forge component (net.minecraftforge.network.PlayMessages$SpawnEntity)

Mixin errors

This does not work for mixin errors (the error text contains mixin): the at lines point to the affected mod, not the culprit. Look for the culprit by the *.mixins.json file name

Old Forge mod table​

Older versions of Forge generated a table with a mods list:

Log example
[:]     | State | ID             | Version      | Source                                    | Signature                                |
[:]     |:----- |:-------------- |:------------ |:----------------------------------------- |:---------------------------------------- |
[:]     | LCH   | minecraft      | 1.12.2       | minecraft.jar                             | None                                     |
[:]     | LCH   | mcp            | 9.42         | minecraft.jar                             | None                                     |
[:]     | LCH   | FML            | 8.0.99.99    | forge-1.12.2-14.23.5.2860.jar             | e3c3d50c7c986df74c645c0ac54639741c90a557 |
[:]     | LCH   | forge          | 14.23.5.2860 | forge-1.12.2-14.23.5.2860.jar             | e3c3d50c7c986df74c645c0ac54639741c90a557 |
[:]     | LCE   | xujmod         | 2.0.8        | xujmod-2.0.8.jar                          | None                                     |

The presence of the letter E in the "State" column signals an error in the mod. For example, in this example xujmod is broken. After removing the broken mods, the game will work.

Forge/NeoForge - missing mod (dependency)​

Many mods need other mods - libraries - to work. If a required mod is missing or its version does not fit, the game will not start. Forge and NeoForge report this in two ways.

NoClassDefFoundError​

Log example
[:] net.minecraftforge.fml.common.LoaderExceptionModCrash: Caught exception from XujMod (xujmod)
[:] Caused by: java.lang.NoClassDefFoundError: blusunrize/immersiveengineering/common/items/ItemIEBase
[:]     at net.lasernet.xuj.ModItems.init(ModItems.java:55)
[:]     at net.lasernet.xuj.XujMod.preInit(XujMod.java:60)

The NoClassDefFoundError error usually signals a missing mod. From this line we can see that the immersiveengineering mod is missing. After installing all required mods the game will work.

However, NoClassDefFoundError does not always mean a missing mod. Look at how the class name from the error starts (some errors use dots instead of /):

  • net/minecraft, net/minecraftforge, net/neoforged, net/fabricmc - this is a class of the game itself or of the mod loader. There is nothing to install: the mod from the error is made for a different game or loader version
  • kotlin/ - install Kotlin for Forge (for Forge and NeoForge) or Fabric Language Kotlin (for Fabric and Quilt)
  • javafx/ - the mod cannot work on the Java the game runs on. Remove it
  • org/lwjgl, io/netty, com/google/common - these are libraries of the game itself. Use the "Force update" checkbox

If the required mod is already installed, update it: the installed version does not have the required class.
If it is unclear which mod is required, search Modrinth for a part of the class name. For example, for blusunrize/immersiveengineering/... search for immersiveengineering

Missing dependencies​

Log example
> [17:01:14] [main/ERROR] [ne.mi.fm.lo.ModSorter/LOADING]: Missing or unsupported mandatory dependencies:
>   Mod ID: 'valhelsia_core', Requested by: 'valhelsia_structures', Expected range: '[1.1.1,)', Actual version: '[MISSING]'
Such lines appear at the beginning of the log

This line shows that the valhelsia_structures mod needs valhelsia_core mod version 1.1.1 or newer, which is not installed now (MISSING). After installing all required mods of required versions the game will start.

Forge/NeoForge - invalid mod name​

After switching the game to Java 17 Forge may crash due to incorrect names of mods. Do not give mods names containing non-Latin characters.

Log example
> Exception in thread "main" java.lang.IllegalArgumentException: 1.0-1.18+: Empty pre-release
>   at java.base/java.lang.module.ModuleDescriptor$Version.<init>(ModuleDescriptor.java:1054)
>   at java.base/java.lang.module.ModuleDescriptor$Version.parse(ModuleDescriptor.java:1090)

By the line 1.0-1.18+: Empty pre-release we can see that Forge cannot understand the line 1.0-1.18+ of some mod. Looking in the mods folder, we find the file lazydfu-1.0-1.18+. After renaming the mod, for example, to lazydfu-1.0, or uninstalling it the game will work.

In newer versions of the game, there is another case:

Log example
> Exception in thread "main" java.lang.IllegalArgumentException: multi-piston: Invalid module name: 'multi-piston' is not a Java identifier
>   at java.base/jdk.internal.module.Checks.requireModuleName(Checks.java:59)

The IllegalArgumentException with the comment Invalid module name indicates an invalid module name for the mod. This usually points to one of two things: either the mod is broken, or the mod is being loaded with the wrong version of the game. There's also a chance the issue lies in the mod's filename. Try renaming the mod (for this example - from multi-piston to multipiston) or remove it

warning

We strongly advise against renaming mod files using non-Latin characters! Some Forge versions will assign empty module names to such mods, causing them to break. It is best to keep the original mod file name

Forge/NeoForge - module conflict​

Since 1.17, Forge and NeoForge load every mod as a separate Java module, and two modules cannot contain the same package. In this case the game crashes with a java.lang.module.ResolutionException error. The order of modules in the message says nothing about the culprit - check which of the named modules are mods you installed.

A mod carries someone else's code​

Log example
> Exception in thread "main" java.lang.module.ResolutionException: Module voicechat.forge contains package org.spongepowered.asm.util.perf, module org.spongepowered.mixin exports package org.spongepowered.asm.util.perf to voicechat.forge
>   at java.base/java.lang.module.Resolver.resolveFail(Resolver.java:901)

Here the Simple Voice Chat mod (voicechat) contains its own copy of Mixin, which the game already has. Download the version of the mod for your game and loader versions or remove the mod

The same code in two files​

Log example
> Exception in thread "main" java.lang.module.ResolutionException: Module optifine contains package srg.net.optifine.entity.model.anim, module OptiFine.OptiFine.HD.U.G8.pre2 exports package srg.net.optifine.entity.model.anim to optifine
>   at java.base/java.lang.module.Resolver.resolveFail(Resolver.java:901)

Here OptiFine is installed twice: as a version with OptiFine and as a separate file in the mods folder. Keep only one copy

Two files of the game itself​

Log example
> Exception in thread "main" java.lang.module.ResolutionException: Modules minecraft and client export package net.minecraft.world.level.levelgen.feature.stateproviders to module mclib
>   at java.base/java.lang.module.Resolver.resolveFail(Resolver.java:901)

If the named modules include no mods you installed, but minecraft and client instead, the installed version has two game files. Reinstall the version using the "Force update" checkbox

Forge/NeoForge - duplicated mods​

If the same mod is in the mods folder twice (e.g. two of its versions), the game will not start. What it looks like in the log depends on the Forge version.

Duplicate interface name error​

Log example
> Exception in thread "main" [16:41:20] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:1069]: java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
> [16:41:20] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:1069]:     at cpw.mods.modlauncher.LaunchServiceHandlerDecorator.launch(LaunchServiceHandlerDecorator.java:39)
> [16:41:20] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:1078]: Caused by: java.lang.reflect.InvocationTargetException
> [16:41:20] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:1078]:     at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
> [16:41:20] [main/INFO] [STDERR/]: [java.lang.Throwable:printStackTrace:659]: Caused by: java.lang.ClassFormatError: Duplicate interface name "xaero/common/minimap/mcworld/IXaeroMinimapClientWorld" in class file net/minecraft/client/world/ClientWorld
> [16:41:20] [main/INFO] [STDERR/]: [java.lang.Throwable:printStackTrace:659]:  at java.base/java.lang.ClassLoader.defineClass1(Native Method)

The java.lang.ClassFormatError: Duplicate interface name ... in class file ... signals us that a mod has been installed twice. After removing the duplicate (the name of the mod usually can be found from the error text, for the example above it is XaeroMinimap) the game will start.

Old Forge versions​

On old Forge versions a duplicate looks like this - the line lists both mod files:

Log example
> [10:58:25] [Client thread/FATAL] [FML]: Found a duplicate mod grapplemod at [D:\Games\Minecraft\files\mods\grapplemod_1.11.2_v10.jar, D:\Games\Minecraft\files\mods\Grappling-Hook-Mod-v13-for-1.12.2.jar]
> [10:58:25] [Client thread/ERROR] [FML]: An exception was thrown, the game will display an error screen and halt.
> net.minecraftforge.fml.common.DuplicateModsFoundException

Here the mods folder contains two versions of the same mod - for 1.11.2 and for 1.12.2. Remove the one that does not match your game version.

New Forge versions​

On newer Forge versions this is reported by the Found duplicate mods line, followed by the Mod ID: '...' from mod files: ... line with both files:

Log example
> [20:50:17] [main/ERROR] [ne.mi.fm.lo.UniqueModListBuilder/LOADING]: Found duplicate mods:
>   Mod ID: 'rubidium' from mod files: rubidium-mc1.20.1-0.7.1.jar, embeddium-0.3.31mc1.20.1.jar
> [20:50:17] [main/ERROR] [ne.mi.fm.lo.mo.ModDiscoverer/SCAN]: Failed to build unique mod list after mod discovery.
> net.minecraftforge.fml.loading.EarlyLoadingException: Duplicate mods found

This error occurs before mods are loaded, so there will be no mod list in the log.

  • If the line lists two versions of the same mod, remove the older one
  • If these are two different mods, they do the same job. In the example above Embeddium replaces Rubidium and therefore calls itself rubidium, and REI Plugin Compatibilities replaces JEI the same way. Keep only one of them

Fabric - broken mod​

Fabric does not always name the mod that crashed the game directly. Below are three typical cases and how to find the culprit in them.

Error when starting a mod​

Log example
> java.lang.RuntimeException: Could not execute entrypoint stage 'main' due to errors, provided by 'bosses_of_mass_destruction'!
>   at net.fabricmc.loader.impl.FabricLoaderImpl.lambda$invokeEntrypoints$2(FabricLoaderImpl.java:388)
>   Suppressed: java.lang.NoClassDefFoundError: Could not initialize class net.barribob.maelstrom.MaelstromMod
>       at net.barribob.maelstrom.MaelstromModKt.init(MaelstromMod.kt:46)

In this log we can see that the bosses_of_mass_destruction mod prevented the game from launching, which in turn was prevented by an error in the Maelstrom mod. After replacing the Maelstrom mod or removing the bosses_of_mass_destruction mod, the error will most likely disappear.

Mixin error​

Log example
> java.lang.RuntimeException: Mixin transformation of net.minecraft.class_372 failed
>   at net.fabricmc.loader.impl.launch.knot.KnotClassDelegate.getPostMixinClassByteArray(KnotClassDelegate.java:427)
> Caused by: org.spongepowered.asm.mixin.transformer.throwables.MixinTransformerError: An unexpected critical error was encountered
>   at org.spongepowered.asm.mixin.transformer.MixinProcessor.applyMixins(MixinProcessor.java:392)
> Caused by: org.spongepowered.asm.mixin.throwables.MixinApplyError: Mixin [sodium-extra.mixins.json:toasts.MixinTutorialToast from mod sodium-extra] from phase [DEFAULT] in config [sodium-extra.mixins.json] FAILED during APPLY
>   at org.spongepowered.asm.mixin.transformer.MixinProcessor.handleMixinError(MixinProcessor.java:638)
> Caused by: org.spongepowered.asm.mixin.injection.throwables.InvalidInjectionException: Invalid descriptor on sodium-extra.mixins.json:toasts.MixinTutorialToast from mod sodium-extra->@Inject::draw(Lnet/minecraft/class_4587;Lnet/minecraft/class_374;JLorg/spongepowered/asm/mixin/injection/callback/CallbackInfoReturnable;)V! Expected (Lnet/minecraft/class_332;Lnet/minecraft/class_374;JLorg/spongepowered/asm/mixin/injection/callback/CallbackInfoReturnable;)V but found (Lnet/minecraft/class_4587;Lnet/minecraft/class_374;JLorg/spongepowered/asm/mixin/injection/callback/CallbackInfoReturnable;)V [INJECT Applicator Phase -> sodium-extra.mixins.json:toasts.MixinTutorialToast from mod sodium-extra -> Apply Injections ->  -> Inject -> sodium-extra.mixins.json:toasts.MixinTutorialToast from mod sodium-extra->@Inject::draw(Lnet/minecraft/class_4587;Lnet/minecraft/class_374;JLorg/spongepowered/asm/mixin/injection/callback/CallbackInfoReturnable;)V]
>   at org.spongepowered.asm.mixin.injection.callback.CallbackInjector.inject(CallbackInjector.java:567)

This time Fabric can't explicitly point us to the problematic mod, but we can recognize it from the error cause message (Caused by:): Caused by: org.spongepowered.asm.mixin.throwables.MixinApplyError: Mixin [sodium-extra.mixins.json:toasts.MixinTutorialToast from mod sodium-extra].
We can see that the problem is the sodium-extra mod (it owns sodium-extra.mixins.json). Most likely, it is made for a different game version - install the version of the mod for your game version or remove it.

Error during gameplay​

Log example
[:] java.lang.NoSuchFieldError: stateTicks
[:]     at com.github.mim1q.minecells.entity.ProtectorEntity.<init>(ProtectorEntity.java:31)
[:]     at net.minecraft.class_1299.method_5883(class_1299.java:544)

This time the error occurred during the game, and Fabric is again unable to detect the problematic mod. But we are lucky - if we read the at lines, we can see that the failure occurred when the minecells mod was running and removing it will most likely solve the issue.

Fabric - mod dependencies​

Fabric mods often require other mods or specific Fabric Loader versions. Usually Fabric checks this before launch and reports what is missing itself - but not always.

Unsuitable versions​

Log example
> net.fabricmc.loader.impl.FormattedException: Some of your mods are incompatible with the game or each other!
> A potential solution has been determined, this may resolve your problem:
>    - Replace mod 'Fabric Loader' (fabricloader) 0.15.7 with any version between 0.14.25 (inclusive) and 0.15- (exclusive).
> More details:
>    - Mod 'GoProne' (goprone) 3.1.3 requires any version between 0.14.21 (inclusive) and 0.15- (exclusive) of mod 'Fabric Loader' (fabricloader), but only the wrong version is present: 0.15.7!
>   at net.fabricmc.loader.impl.FormattedException.ofLocalized(FormattedException.java:51) ~[fabric-loader-0.15.7.jar:?]

You must install mods that meet the requirements of the installed mods.
For example, in this case a mod requires a version of Fabric Loader 0.14.25 or newer, but older than 0.15, making it unsuitable for the version 0.15.7 you are using. Updating the mod or installing the required version of fabric-loader will fix this problem.

Indium​

On Sodium before 0.6.0, mods using the Fabric Rendering API crash if the Indium mod is not installed:

Log example
> Caused by: java.lang.NullPointerException: Cannot invoke "net.fabricmc.fabric.api.renderer.v1.Renderer.meshBuilder()" because the return value of "net.fabricmc.fabric.api.renderer.v1.RendererAccess.getRenderer()" is null
>   at me.pepperbell.continuity.impl.client.ProcessingContextImpl.<init>(ProcessingContextImpl.java:20) ~[continuity-3.0.0+1.19.4.jar:?]

The key line is RendererAccess.getRenderer() in the NullPointerException text. Install Indium, there is no need to remove the crashed mod (continuity here).

note

Since Sodium 0.6.0 Indium is not needed, and this error is no longer relevant

Corrupted files​

Mod corruption​

Files of mods and of the game itself may get corrupted or go missing - due to an interrupted download, an antivirus or disk problems.

Corrupted file​

Log example
Exception in thread "main" cpw.mods.niofs.union.UnionFileSystem$UncheckedIOException: java.util.zip.ZipException: zip END header not found
Caused by: java.util.zip.ZipException: zip END header not found
    at jdk.zipfs/jdk.nio.zipfs.ZipFileSystem.findEND(ZipFileSystem.java:1315)

The java.util.zip.ZipException: zip END header not found error in the log signals that the game files and/or mods are corrupted. Use the "Force update" checkbox, re-download mods from CurseForge/Modrinth.
If the files turn out to be corrupted again after downloading, check your disk for errors.

Fabric and Quilt specifics

Fabric and Quilt store some data in the .fabric and .cache folders in the game folder. If the error points to a file from these folders, delete the folder - the loader will recreate it. Re-downloading such a file is useless

Missing file​

Sometimes the required file is missing entirely - most often it was deleted by an antivirus or the download was interrupted:

Log example
> Exception in thread "main" java.lang.module.FindException: Module org.apache.logging.log4j not found, required by cpw.mods.modlauncher
>   at java.base/java.lang.module.Resolver.findFail(Resolver.java:893)
Log example
15:46:36,709 [MinecraftLauncher] Caught an exception
net.legacylauncher.minecraft.launcher.MinecraftException: Classpath is not found: D:\Minecraft\Minecraft\game\libraries\at\yawk\lz4\lz4-java\1.8.1\lz4-java-1.8.1.jar
    at net.legacylauncher.minecraft.launcher.MinecraftLauncher.constructClassPath(MinecraftLauncher.java:1484)

Use the "Force update" checkbox. If the files disappear again, check your antivirus.

Config files corruption​

Log example
> net.minecraftforge.fml.config.ConfigFileTypeHandler$ConfigLoadingException: Failed loading config file flywheel-client.toml of type CLIENT for modid flywheel
>   at net.minecraftforge.fml.config.ConfigFileTypeHandler.lambda$reader$1(ConfigFileTypeHandler.java:47) ~[forge:?] {re:classloading}
>   at net.minecraftforge.fml.config.ConfigTracker.openConfig(ConfigTracker.java:90) ~[forge:?] {re:classloading}
> Caused by: com.electronwill.nightconfig.core.io.ParsingException: Not enough data available
>   at com.electronwill.nightconfig.core.io.ParsingException.notEnoughData(ParsingException.java:22) ~[core-3.6.3.jar:?] {}

Such errors are usually recognized by the presence of the word "config" or "settings" in the error. In this example you can see that the flywheel-client.toml config file of the flywheel mod is broken.
Such problems are solved very simply - by deleting the corresponding file from the config folder in the game folder, or by deleting the entire config folder - the mods will recreate their settings files.
If you have the original config folder (e.g. in the modpack archive), it is better to replace the current one with it.
Some mods keep part of their settings in the world folder: if the file is not in the config folder, look for it in saves/<world name>/serverconfig.