I've gotten this error trying to use magiclauncher to install Forge.  Vanilla unmodded minecraft 1.4.5, magiclauncher 1.0.0, and forge version 1.4.5-6.4.0.396 (which is the current recommended build.)  I am not running any other mods of any type, in fact, i just completely wiped my .minecraft folder from %appdata%, and reinstalled fresh, and am still getting this error

 

Any other info needed, just ask.

 

Log file

 

 

MagicLauncher 1.0.0

java.home: C:\Program Files\Java\jre7

java.runtime.name: Java SE Runtime Environment

java.runtime.version: 1.7.0_07-b11

os.name: Windows 7

os.version: 6.1

os.arch: x86

sun.arch.data.model: 32

Missing class member: public B c, class: ahg, mod: minecraftforge-universal-1.4.5-6.4.0.396(1).zip

Missing class member: public B c, class: ahg, mod: minecraftforge-universal-1.4.5-6.4.0.396.zip

 

*** Starting Minecraft ***

Minecraft version: 1.4.5

Minecraft.jar: minecraft.jar

Mods:

  minecraftforge-universal-1.4.5-6.4.0.396.zip

Show log: true

Java path: C:\Program Files\Java\jre7\bin\java

Memory: 512 MB

LauncherPath: /C:/Users/darva/Downloads/MagicLauncher_1.0.0.exe

*** MagicMinecraftLauncher 1.0.0 ***

java.lang.IncompatibleClassChangeError: Implementing class

    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 magic.launcher.Launcher.main(Unknown Source)

 

 

 

magiclauncher.cfg

 

 

<Profile

  <Name="Default">

  <MinecraftJar="C:\\Users\\darva\\AppData\\Roaming\\.minecraft\\bin\\minecraft.jar">

  <ShowLog="true">

  <MaxMemory="512">

  <Mod

    <File="C:\\Users\\darva\\Downloads\\minecraftforge-universal-1.4.5-6.4.0.396(1).zip">

    <Active="true">

  >

>

<ActiveProfileIndex="0">

<LastModDir="C:\\Users\\darva\\Downloads">

<LoadNews="true">

 

 

 

Don't use magiclauncher. Use MultiMC.

So i checked on my laptop, installed everything in exactly the same way i did on my desktop.  It bloody works.  The only difference between the two is that the laptop runs 64 bit windows, and the desktop runs 32 bit, and that the laptop hadn't had minecraft installed previously.  (But that shouldn't matter, as i completely deleted and reinstalled minecraft on the desktop.)

 

I am truly at a loss.  However, since it's working on the laptop with magiclauncher, i don't see how magiclauncher could be the culprit.

Get rid of the (1) in the name of the forge jar..