/ICustomItemRenderer and ClassNotFoundException error

Mods loaded: 21
ModLoader 1.2.3
mod_MinecraftForge 1.4.1.58
mod_ModLoaderMp 1.2.3v3
mod_betterDungeons 0.921
mod_BuildCraftCore 3.1.4
mod_BuildCraftBuilders 3.1.4
mod_BuildCraftEnergy 3.1.4
mod_BuildCraftFactory 3.1.4
mod_IC2 v1.81
mod_MoreExplosives Release 1.5 for Minecraft 1.1
mod_PortalGun 1.2.3v1
mod_Railcraft 4.0.0
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_Arrows303 1.2.3 AS
mod_ASGrapplingHook 1.2.3 AS

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

Minecraft has stopped running because it encountered a problem.

--- BEGIN ERROR REPORT 36792747 --------
Generated 3/20/12 9:24 AM

Minecraft: Minecraft 1.2.3
OS: Windows 7 (amd64) version 6.1
Java: 1.7.0_04-ea, Oracle Corporation
VM: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
LWJGL: 2.4.2
OpenGL: Intel(R) HD Graphics Family version 3.1.0 - Build 8.15.10.2622, Intel

java.lang.NoClassDefFoundError: forge/ICustomItemRenderer
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(Unknown Source)
at java.security.SecureClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.access$100(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at mod_PortalGun.initModPart(mod_PortalGun.java:359)
at mod_PortalGun.initModParts(mod_PortalGun.java:256)
at mod_PortalGun.load(mod_PortalGun.java:137)
at ModLoader.init(ModLoader.java:890)
at ModLoader.addAllRenderers(ModLoader.java:186)
at aho.<init>(aho.java:79)
at aho.<clinit>(aho.java:9)
at net.minecraft.client.Minecraft.a(Minecraft.java:395)
at net.minecraft.client.Minecraft.run(Minecraft.java:732)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.ClassNotFoundException: forge.ICustomItemRenderer
at java.net.URLClassLoader$1.run(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
... 21 more
--- END ERROR REPORT b297dad6 ----------