Coremod works in eclipse, but not on minecraft [1.6.4]

heyo all,

i got a problem while making a custom menu for a modpack:

when i start the mod it shows this

18:01:54 INFO]: Client> 2014-04-03 18:01:54 [infos] [ForgeModLoader] Calling tweak class cpw.mods.fml.relauncher.CoreModManager$FMLPluginWrapper

[18:01:54 INFO]: Client> 2014-04-03 18:01:54 [infos] [sTDOUT] *** Transformer jar location location.getName: Happy Diggers Custom Menu.jar

[18:01:54 INFO]: Client> 2014-04-03 18:01:54 [infos] [ForgeModLoader] Calling tweak class cpw.mods.fml.common.launcher.FMLDeobfTweaker

[18:01:54 INFO]: Client> 2014-04-03 18:01:54 [infos] [ForgeModLoader] Launching wrapped minecraft {net.minecraft.client.main.Main}

[18:01:55 INFO]: Client> 2014-04-03 18:01:55 [infos] [sTDOUT] ********* Main Menu ABOUT TO PATCH: blt

[18:01:55 INFO]: Client> 2014-04-03 18:01:55 [infos] [sTDOUT] [Happy Diggers Custom Menu]: Class blt patched!

[18:01:55 INFO]: Client> 2014-04-03 18:01:55 [Grave] [ForgeModLoader] Unable to launch

[18:01:55 INFO]: Client> java.lang.reflect.InvocationTargetException

[18:01:55 INFO]: Client> at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

[18:01:55 INFO]: Client> at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)

[18:01:55 INFO]: Client> at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)

[18:01:55 INFO]: Client> at java.lang.reflect.Method.invoke(Unknown Source)

[18:01:55 INFO]: Client> at net.minecraft.launchwrapper.Launch.launch(Launch.java:131)

[18:01:55 INFO]: Client> at net.minecraft.launchwrapper.Launch.main(Launch.java:27)

[18:01:55 INFO]: Client> Caused by: java.lang.NoClassDefFoundError: net/minecraft/client/gui/GuiMainMenu

[18:01:55 INFO]: Client> at net.minecraft.client.main.Main.main(SourceFile:37)

[18:01:55 INFO]: Client> ... 6 more

[18:01:55 INFO]: Client> Caused by: java.lang.ClassNotFoundException: net.minecraft.client.gui.GuiMainMenu

[18:01:55 INFO]: Client> at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:186)

[18:01:55 INFO]: Client> at java.lang.ClassLoader.loadClass(Unknown Source)

[18:01:55 INFO]: Client> at java.lang.ClassLoader.loadClass(Unknown Source)

[18:01:55 INFO]: Client> ... 7 more

[18:01:55 INFO]: Client> Caused by: java.lang.NullPointerException

[18:01:55 INFO]: Client> at org.objectweb.asm.Type.getType(Unknown Source)

[18:01:55 INFO]: Client> at org.objectweb.asm.commons.Remapper.mapDesc(Unknown Source)

[18:01:55 INFO]: Client> at org.objectweb.asm.commons.RemappingMethodAdapter.visitLocalVariable(Unknown Source)

[18:01:55 INFO]: Client> at org.objectweb.asm.ClassReader.a(Unknown Source)

[18:01:55 INFO]: Client> at org.objectweb.asm.ClassReader.b(Unknown Source)

[18:01:55 INFO]: Client> at org.objectweb.asm.ClassReader.accept(Unknown Source)

[18:01:55 INFO]: Client> at org.objectweb.asm.ClassReader.accept(Unknown Source)

[18:01:55 INFO]: Client> at cpw.mods.fml.common.asm.transformers.DeobfuscationTransformer.transform(DeobfuscationTransformer.java:39)

[18:01:55 INFO]: Client> at net.minecraft.launchwrapper.LaunchClassLoader.runTransformers(LaunchClassLoader.java:274)

[18:01:55 INFO]: Client> at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:172)

[18:01:55 INFO]: Client> ... 9 more

[18:01:55 INFO]: Game ended with no troubles detected (exit code 0)

[18:01:55 INFO]: Deleting C:\Users\Frederic\AppData\Roaming\.minecraft\versions\1.6.4-Forge9.11.1.965\1.6.4-Forge9.11.1.965-natives-825320752765261

the modded class is GuiMainMenu

here is the jar i use http://www.mediafire.com/download/rh0wvf7bab2dl0m/Happy_Diggers_Custom_Menu.jar

and the scr http://www.mediafire.com/download/402k8f07u6yktub/content_scr_coremod.zip

(feel free to use it)

what i do want is replace the original GuiMainMenu.class with this one, i hope someone can help me