I have tried multiple versions of forge and I keep getting this error. I have tried a 3.0.x version and 3.1.3.105.

Log from MagicLauncer:

 

 

MagicLauncher 0.9.7

java.home: C:\Program Files\Java\jre6

java.runtime.name: Java SE Runtime Environment

java.runtime.version: 1.6.0_31-b05

os.name: Windows 7

os.version: 6.1

os.arch: amd64

sun.arch.data.model: 64

com.sun.org.apache.xerces.internal.impl.io.MalformedByteSequenceException: Invalid byte 1 of 1-byte UTF-8 sequence.

    at com.sun.org.apache.xerces.internal.impl.io.UTF8Reader.invalidByte(Unknown Source)

    at com.sun.org.apache.xerces.internal.impl.io.UTF8Reader.read(Unknown Source)

    at com.sun.org.apache.xerces.internal.impl.XMLEntityScanner.load(Unknown Source)

    at com.sun.org.apache.xerces.internal.impl.XMLEntityScanner.scanData(Unknown Source)

    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanCDATASection(Unknown Source)

    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(Unknown Source)

    at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(Unknown Source)

    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source)

    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source)

    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source)

    at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(Unknown Source)

    at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(Unknown Source)

    at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(Unknown Source)

    at javax.xml.parsers.SAXParser.parse(Unknown Source)

    at javax.xml.parsers.SAXParser.parse(Unknown Source)

    at magic.launcher.af.run(Unknown Source)

Missing class member: public (Lxd;IIIIFI)V a, class: jx, mod: minecraftforge-client-3.1.2.90.zip

Missing class member: public (Lxd;IIIIFI)V a, class: rr, mod: minecraftforge-client-3.1.2.90.zip

 

*** Starting Minecraft ***

Minecraft version: 1.2.5

Minecraft.jar: minecraft.jar

Mods:

  ModLoader.zip

  AudioMod.zip

  minecraftforge-client-3.1.2.90.zip

  ModLoaderMP 1.2.5 v1.zip

  4096-Fix-v4.2-mc1.2.5.zip

  NotEnoughItems-Client 1.2.2.zip

  CodeChickenCore-Client 0.5.2.zip

  buildcraft-C-additionalbuildcraftobjects-f122bc227-38.zip

  CraftingTableIIIB1.2.zip

  EE2ModV1.4.4.0.jar

  EnderStorage-Client 1.1.1.zip

  industrialcraft-2-client_1.95b.jar

  InvTweaks-1.41b-1.2.4.zip

  Laser Mod 1.5.zip

  LogisticsPipes-BC3-0.2.5A.zip

  mod_compactsolars-client-2.2.0.5.zip

  mod_ironchests-client-3.3.1.21.zip

  SneakyPipes-0.1.1.zip

Java path: C:\Program Files\Java\jre6\bin\java

Memory: 1024 MB

LauncherPath: /S:/Archive/Downloads/MagicLauncher_0.9.7.exe

*** MagicMinecraftLauncher 0.9.7 ***

27 achievements

182 recipes

LWJGL Version: 2.4.2

ModLoader 1.2.5 Initializing...

Register ModLoader mods

Mod Initialized: mod_MinecraftForge 3.1.2.90

Mod Initialized: mod_ModLoaderMp 1.2.5v1

Mod Initialized: mod_4096Fix v4 for 1.2.5

Mod Initialized: mod_NotEnoughItems 1.2.2

Mod Initialized: mod_CodeChickenCore 0.5.2

Failed to load mod from "mod_AdditionalBuildcraftObjects.class"

MinecraftForge v3.1.2.90 Initialized

May 6, 2012 2:41:41 PM forge.ForgeHooks <clinit>

INFO: MinecraftForge v3.1.2.90 Initialized

 

Equals

Test: true

Mod Initialized: mod_CraftingTableIII (Beta1.2, MC1.2.5)

Initializing alchemy values for Equivalent Exchange..

Mod Initialized: mod_EE 1.4.4.0

Mod Initialized: mod_EnderStorage 1.1.1

Mod Initialized: mod_IC2 v1.95

Mod Initialized: mod_InvTweaks 1.41b (1.2.4)

Mod Initialized: mod_PigbearLaser 1.4

Failed to load mod from "mod_LogisticsPipes.class"

Mod Initialized: mod_CompactSolars 2.2

Mod Initialized: mod_IronChest 3.3

Mod Initialized: mod_SneakyPipes 0.1.1 (Minecraft 1.2.5, Buildcraft 3.1.5, Forge 3.0.1.75)

Restoring disabled mods

Failed to load mod from "mod_BuildCraftCore.class"

Failed to load mod from "mod_BuildCraftBuilders.class"

Failed to load mod from "mod_BuildCraftEnergy.class"

Failed to load mod from "mod_BuildCraftFactory.class"

Failed to load mod from "mod_BuildCraftTransport.class"

Failed to load mod from "mod_BuildCraftSilicon.class"

Mod Initialized: mod_RedPowerControl 2.0pr5b1

Mod Initialized: mod_RedPowerCore 2.0pr5b1

Mod Initialized: mod_RedPowerLighting 2.0pr5b1

Mod Initialized: mod_RedPowerLogic 2.0pr5b1

Mod Initialized: mod_RedPowerMachine 2.0pr5b1

Mod Initialized: mod_RedPowerWiring 2.0pr5b1

Mod Initialized: mod_RedPowerWorld 2.0pr5b1

Mod Loaded: mod_CodeChickenCore 0.5.2

Mod Loaded: mod_MinecraftForge 3.1.2.90

Mod Loaded: mod_ModLoaderMp 1.2.5v1

Mod Loaded: mod_4096Fix v4 for 1.2.5

Mod Loaded: mod_NotEnoughItems 1.2.2

Mod Loaded: mod_CraftingTableIII (Beta1.2, MC1.2.5)

Mod Loaded: mod_EE 1.4.4.0

CONFLICT @ 2410

Mod Loaded: mod_EnderStorage 1.1.1

[iC2] Config loaded from C:\Users\Kayler\AppData\Roaming\.minecraft\config\IC2.cfg

[iC2] Using 32 audio sources.

Mod Loaded: mod_IC2 v1.95

Mod Loaded: mod_InvTweaks 1.41b (1.2.4)

210

213

Mod Loaded: mod_PigbearLaser 1.4

Mod Loaded: mod_CompactSolars 2.2

IronChest: MinecraftForge minor version mismatch, expecting 3.0.x, may lead to unexpected behavior

Mod Loaded: mod_IronChest 3.3

Mod Loaded: mod_RedPowerControl 2.0pr5b1

Mod Loaded: mod_RedPowerCore 2.0pr5b1

Mod Loaded: mod_RedPowerLighting 2.0pr5b1

Mod Loaded: mod_RedPowerLogic 2.0pr5b1

Mod Loaded: mod_RedPowerMachine 2.0pr5b1

Mod Loaded: mod_RedPowerWiring 2.0pr5b1

Mod Loaded: mod_RedPowerWorld 2.0pr5b1

ModLoaderMP 1.0.0 Initialized

[iC2] Loading IC2 submodule: bcIntegration31x

[iC2] Submodule not loaded: java.lang.reflect.InvocationTargetException: java.lang.NoClassDefFoundError: Could not initialize class buildcraft.api.BuildCraftAPI

[iC2] Loading IC2 submodule: bcIntegration22x

[iC2] BuildCraft integration module loaded

[iC2] Loading IC2 submodule: cgIntegration14x

[iC2] Submodule not loaded: java.lang.reflect.InvocationTargetException: java.lang.NoClassDefFoundError: CraftGuide/API/IRecipeProvider

[iC2] Loading IC2 submodule: neiIntegration11x

[iC2] NEI integration module loaded

[iC2] Portal Gun compatibility not loaded: java.lang.ClassNotFoundException: mod_PortalGun

May 6, 2012 2:41:42 PM mod_CompactSolars modsLoaded

INFO: Compact Solar (2.2) rev 0 build 5 loaded successfully.

Done.

Restoring disabled mods

WARNING: Found unknown Windows version: Windows 7

Attempting to use default windows plug-in.

Loading: net.java.games.input.DirectAndRawInputEnvironmentPlugin

 

Starting up SoundSystem...

Initializing LWJGL OpenAL

    (The LWJGL binding of OpenAL.  For more information, see http://www.lwjgl.org)

OpenAL initialized.

 

 

 

Minecraft crash log:

 

 

Mods loaded: 15

ModLoader 1.2.5

mod_MinecraftForge 3.1.2.90

mod_ModLoaderMp 1.2.5v1

mod_4096Fix v4 for 1.2.5

mod_NotEnoughItems 1.2.2

mod_CodeChickenCore 0.5.2

mod_CraftingTableIII (Beta1.2, MC1.2.5)

mod_EE 1.4.4.0

mod_EnderStorage 1.1.1

mod_IC2 v1.95

mod_InvTweaks 1.41b (1.2.4)

mod_PigbearLaser 1.4

mod_CompactSolars 2.2

mod_IronChest 3.3

mod_SneakyPipes 0.1.1 (Minecraft 1.2.5, Buildcraft 3.1.5, Forge 3.0.1.75)

 

      Minecraft has crashed!     

      ----------------------     

 

Minecraft has stopped running because it encountered a problem.

 

--- BEGIN ERROR REPORT baa62899 --------

Generated 5/6/12 2:41 PM

 

Minecraft: Minecraft 1.2.5

OS: Windows 7 (amd64) version 6.1

Java: 1.6.0_31, Sun Microsystems Inc.

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

LWJGL: 2.4.2

OpenGL: AMD Radeon HD 7900 Series version 4.2.11631 Compatibility Profile Context, ATI Technologies Inc.

 

java.lang.NoClassDefFoundError: forge/ICustomItemRenderer

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

at java.lang.ClassLoader.defineClassCond(Unknown Source)

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$000(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 ModLoader.addMod(ModLoader.java:289)

at ModLoader.readFromModFolder(ModLoader.java:1276)

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(Unknown Source)

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

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)

... 20 more

--- END ERROR REPORT 28c80b6e ----------

 

Sounds like a mod is outdated and is trying to use ICustomItemRenderer while it's deprecated.