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  • There is an installer for 1.6.x versions and above of Forge. USE IT, it will solve 80% of all your problems. Do not use the universal install.
  • Failure to comply with the rules in this EAQ means your thread will be locked.
  • DO NOT ask for help with any version besides the latest MC version. If you are using a modpack, please ask your modpack maker (FTB/Technic/whatever)
  • No two problems are alike. DO NOT post in an existing thread if you have the same problem, make a new one.
  • Support for legacy versions of MC and Forge will not be offered. Instructions in this thread is all you'll get, if not you're on your own.
  • Support for "cracked" / "pirated" launchers will not be offered and you will be banned. Buy the game.
  • Support with mods that edit base files ("drag this into the minecraft jar") will not be offered.



Things to do before you post:

  • THIS IS A SUPPORT FORUM FOR FML/FORGE, AND ONLY FML/FORGE. Go to a mod specific forum (whether on this site or another) to ask for help with a certain mod. If you are using MCPC+/Cauldron or any other Bukkit-API server software, do not post here, post in their forums. For help with Sponge, go here.
  • This is a support forum for players, not for modders needing help with code. Modders go to the Modder Support forum.
  • Search for your issue (the first line of the stack trace is a good start). Do not reply to threads you think are related to your issue.
  • If you think you have found a bug, please retry with the latest forge build available from http://files.minecraftforge.net before posting here.
  • Read the "Common Problems and Solutions" section below.
  • If you need help writing a bug report/support request, go here: http://vazkii.us/br101/
  • Make sure you have not installed either ModLoader or MCPatcher (use Optifine instead).
  • If the top line of your error log does not contain net.minecraftforge.whatever or cpw.mods.fml.something, the reason is most likely not Forge, it's an issue with the mod you're using.
  • Make sure you have read the installation instructions for the mods you use. Mods often require certain other mods to function or require a specific version of Forge.


Below is a list of things which you MUST include in your post.

  • Be sure to include the entire logs/debug.log (logs/fml-{client/server}-latest.log for versions before 2629) found in your .minecraft folder / server root folder. Not including the log in no way helps us to help you and has a small chance of getting you banned.
  • State what research you have already done (You should have done some, this forum is only for well-researched bugs!).
  • Use the spoilers to enclose stack traces and other long information: HhfZh7s.png
  • Do not attach your logs to your post or use file-uploading services like Dropbox. Use Pastebin or Github Gists.
  • In general give as much information as you can. "It does not work", "I get a black Screen", etc. in no way helps us to help you and will only cause you to get in trouble. :)


Edited by diesieben07
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Common Problems and Solutions:

  • java.lang.UnsupportedClassVersionError: ******** : Unsupported major.minor version 51.0 or 52.0 - Use Java 8. Not 7 or even 6.
  • java.lang.ClassCastException: java.base/jdk.internal.loader.ClassLoaders$AppClassLoader cannot be cast to java.base/java.net.URLClassLoader - Use Java 8.
  • java.lang.OutOfMemoryError: PermGen space: Update to Java 8 or increase your PermGen Space with the following command line argument: -XX:MaxPermSize=256m.
  • java.lang.NullPointerException with com.pclewis.mcpatcher.mod.something: For the love of god, don't use MCPatcher. Use OptiFine instead.
  • If you can't run the installer and are on Windows, try Jarfix first. Download it, and run it. If you're using the .exe ones, DISABLE YOUR 3RDPARTY ANTIVIRUS and try running the installer again.
  • It is highly recommended you run any modded versions in separate folders using the GameDirectory setting in the vanilla launcher. This will store all your save files, configs, mods, etc. in whatever folder you specify (instead of just .minecraft) so they do not interfere with your vanilla installation (or other modded versions you may have installed) and vice versa. To set it, click "Edit Profile" in your launcher and in the settings screen that pops up, modify the "Game Directory" setting (Screenshot).
  • If you are using an Intel GPU and Minecraft freezes during loading, disable the loading screen by setting "enabled" to "false" in .minecraft/config/splash.properties.
  • This version of FML is built for Minecraft a.b.c, we have detected Minecraft x.y.z in your minecraft jar file: Do as it says and get the FML/Forge versions for x.y.z.
  • "You need to run the version X manually once." This means that you have to run VANILLA minecraft (no mods) for the version listed before you can install Forge.
  • These libraries failed to download. Try again. org.scala-lang:scala-library:2.10.2, org.scala-lang:scala-compiler:2.10.2
    Download this: https://bitbucket.org/luacs1998/forgelibrarydownloads/downloads/fmllibs16.zip and extract it to your .minecraft folder, then try running Minecraft, or redownload the installer.
    Otherwise, we will need console logs, and your JVM and OS versions.
  • java.lang.NoClassDefFoundException: net/minecraft/client/something : One of your mods is client only and you're on a dedicated server. Check which ones, and remove them.
  • io.netty.channel.ChannelException: failed to open a new selector: Update to version or above. Previous versions: Add -Djava.net.preferIPv4Stack=true to your VM args.
  • java.lang.ConcurrentModificationException or java.util.ConcurrentModificationException before Minecraft loads: Update forge.
  • java.lang.IndexOutOfBoundsException
    at java.nio.Buffer.checkIndex
    at java.nio.DirectIntBufferU.get
    at net.minecraft.client.renderer.RenderGlobal...
    - Lower your view distance.
  • java.net.SocketException or blank dirt screen when connecting to a server: Ensure the client and server configs match.
  • If your text is distorted like seen below (or you have been instructed to do so), disable the loading screen by setting "enabled" to "false" in .minecraft/config/splash.properties.


  • If your main menu background is compressed to a corner, and the rest of the menu is black/white: Update your Forge to at least or add -Dforge.forceNoStencil=true to the VM arguments in the launcher.
  • If MagicLauncher tells you there are errors in forge:
    On 2.12.2012 at 11:36 AM, LexManos said:
    Dont trust MagicLaunchers BS, it lies.
Edited by diesieben07
add info about java versions > 8
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Solutions for pre-1.6 problems:


  • If you are using 1.5:
    Download the file you need from https://files.minecraftforge.net/fmllibs.zip (extract to .minecraft), or re-run your forge installer.
  • java.lang.NoClassDefFoundError: aux (for Windows users only): DO NOT extract the minecraft.jar. Some Windows bug prevents a file from being named aux.class. You'll need to get a proper archive manager (I recommend 7zip) or get a launcher or mod manager.
  • java.lang.NoSuchMethodFoundException: ofCustomFonts - Install Optifine after forge. It already says so in their forum topic.
  • java.lang.IllegalAccessError: tried to access field xy.z from class net.minecraftforge.something: Check your minecraft.jar or forge.jar to see if you have the fml_at.cfg and forge_at.cfg files. They are required to allow FML and Forge to work.
  • NoClassDefFoundError: cpw/mods/fml/common/asm/ASMTransformer: Clean your entire coremods folder.


This may be expanded on later, make sure to read updates.

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