[Missing Class File?]

I get this error when I try to run Minecraft, with BuildCraft and IC2. It seems I'm missing a class file, it says.

 

 

Mods loaded: 2

ModLoader 1.2.5

mod_MinecraftForge 3.1.3.102

 

      Minecraft has crashed!   

      ----------------------     

 

Minecraft has stopped running because it encountered a problem.

 

 

 

--- BEGIN ERROR REPORT 3fa24a14 --------

Generated 4/29/12 3:45 PM

 

Minecraft: Minecraft 1.2.5

OS: Mac OS X (x86_64) version 10.6.8

Java: 1.6.0_31, Apple Inc.

VM: Java HotSpot 64-Bit Server VM (mixed mode), Apple Inc.

LWJGL: 2.4.2

OpenGL: ATI Radeon HD 2400 XT OpenGL Engine version 2.1 ATI-1.6.36, ATI Technologies Inc.

 

java.lang.NoClassDefFoundError: forge/ICustomItemRenderer

at java.lang.ClassLoader.defineClass1(Native Method)

at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631)

at java.lang.ClassLoader.defineClass(ClassLoader.java:615)

at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)

at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)

at java.net.URLClassLoader.access$000(URLClassLoader.java:58)

at java.net.URLClassLoader$1.run(URLClassLoader.java:197)

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)

at ModLoader.addMod(ModLoader.java:289)

at ModLoader.readFromModFolder(ModLoader.java:1292)

at ModLoader.init(ModLoader.java:887)

at ModLoader.addAllRenderers(ModLoader.java:189)

at ahu.<init>(ahu.java:77)

at ahu.<clinit>(ahu.java:

at net.minecraft.client.Minecraft.a(Minecraft.java:394)

at net.minecraft.client.Minecraft.run(Minecraft.java:732)

at java.lang.Thread.run(Thread.java:680)

Caused by: java.lang.ClassNotFoundException: forge.ICustomItemRenderer

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)

... 20 more

--- END ERROR REPORT 7df605 ----------