Crash mincraft modlear

Bonjour, j'ai essayer d installer un game mode avec mon Mac et puis depuis que j au tellecharger modlear mon minecraft crash il met :

Minecraft has crashed!
----------------------

Minecraft has stopped running because it encountered a problem; Exception occured in ModLoader
This error has been saved to /Users/dominic/Library/Application Support/minecraft/crash-reports/crash-2012-08-07_13.07.45-client.txt for your convenience. Please include a copy of this file if you report this crash to anyone.

--- BEGIN ERROR REPORT 5d1a30d2 --------
Generated 07/08/12 13:07

- Minecraft Version: 1.3.1
- Operating System: Mac OS X (x86_64) version 10.7.4
- Java Version: 1.6.0_31, Apple Inc.
- Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Apple Inc.
- Memory: 497089632 bytes (474 MB) / 534708224 bytes (509 MB) up to 1065025536 bytes (1015 MB)
- JVM Flags: 3 total; -Xbootclasspath/a:/System/Library/PrivateFrameworks/JavaApplicationLauncher.framework/Resources/LauncherSupport.jar -Xms512M -Xmx1024M
- ModLoader: Mods loaded: 1
ModLoader 1.3.1

java.lang.NoClassDefFoundError: xg
at java.lang.Class.getDeclaredFields0(Native Method)
at java.lang.Class.privateGetDeclaredFields(Class.java:2291)
at java.lang.Class.getDeclaredFields(Class.java:1743)
at ModLoader.setupProperties(ModLoader.java:2048)
at ModLoader.addMod(ModLoader.java:326)
at ModLoader.readFromClassPath(ModLoader.java:1317)
at ModLoader.init(ModLoader.java:915)
at ModLoader.addAllRenderers(ModLoader.java:169)
at avx.<init>(RenderManager.java:86)
at avx.<clinit>(RenderManager.java:12)
at net.minecraft.client.Minecraft.a(SourceFile:260)
at net.minecraft.client.Minecraft.run(SourceFile:516)
at java.lang.Thread.run(Thread.java:680)
Caused by: java.lang.ClassNotFoundException: xg
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
... 13 more
--- END ERROR REPORT c4a59950 ----------