Hi! I posted this error on the modloader page, and they told me it was a IC error. Derp.
This actually works if I uninstall buildcraft though, which is odd.
Mods loaded: 24
ModLoader 1.2.3
mod_ModLoaderMp 1.2.3v3
mod_NotEnoughItems 1.1.3
mod_GuiApiBasicExample 1.1
mod_GuiApiIntermediateExample 1.0
mod_GuiApiItemTickExample 1.0
mod_GuiApiTWLExamples 1.0
mod_4096IDs version 1.0.1 for MC 1.2.3
mod_MinecraftForge 1.4.0.55
mod_BuildCraftCore 3.1.4
mod_BuildCraftBuilders 3.1.4
mod_BuildCraftEnergy 3.1.4
mod_BuildCraftFactory 3.1.4
mod_BuildCraftTransport 3.1.4
mod_BuildCraftSilicon 3.1.4
mod_IC2 v1.81
mod_RedPowerArray 2.0pr4d
mod_RedPowerCore 2.0pr4e
mod_RedPowerLighting 2.0pr4e
mod_RedPowerLogic 2.0pr4e
mod_RedPowerMachine 2.0pr4e
mod_RedPowerWiring 2.0pr4e
mod_RedPowerWorld 2.0pr4e
mod_IDResolver 1.2.3 - Update 0
Minecraft has crashed!
----------------------
Minecraft has stopped running because it encountered a problem.
--- BEGIN ERROR REPORT f3c2b8b5 --------
Generated 19/03/12 11:46 AM
Minecraft: Minecraft 1.2.3
OS: Windows Vista (x86) version 6.0
Java: 1.6.0_31, Sun Microsystems Inc.
VM: Java HotSpot™ Client VM (mixed mode), Sun Microsystems Inc.
LWJGL: 2.4.2
OpenGL: ATI Mobility Radeon HD 2400 XT version 2.1.7981 Release, ATI Technologies Inc.
java.lang.ArrayIndexOutOfBoundsException: -3591
at ym.<init>(Item.java:208)
at uz.<init>(ItemBlock.java:12)
at ModLoader.registerBlock(ModLoader.java:1480)
at ModLoader.registerBlock(ModLoader.java:1459)
at mod_IC2.load(mod_IC2.java:205)
at ModLoader.init(ModLoader.java:858)
at ModLoader.addAllRenderers(ModLoader.java:151)
at aho.<init>(aho.java:79)
at aho.<clinit>(aho.java:9)
--- END ERROR REPORT 20ff235c ----------