Mod wont load in?

Whenever i run my mod within the test environment from eclipse everything works fine, but as soon as i try to build the mod and install it in my modsfolders this happens:

java.lang.NoClassDefFoundError: net/minecraft/command/ICommand
	at java.lang.Class.forName0(Native Method)
	at java.lang.Class.forName(Class.java:344)
	at cpw.mods.fml.common.FMLModContainer.constructMod(FMLModContainer.java:440)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:483)
	at com.google.common.eventbus.EventSubscriber.handleEvent(EventSubscriber.java:74)
	at com.google.common.eventbus.SynchronizedEventSubscriber.handleEvent(SynchronizedEventSubscriber.java:47)
	at com.google.common.eventbus.EventBus.dispatch(EventBus.java:322)
	at com.google.common.eventbus.EventBus.dispatchQueuedEvents(EventBus.java:304)
	at com.google.common.eventbus.EventBus.post(EventBus.java:275)
	at cpw.mods.fml.common.LoadController.sendEventToModContainer(LoadController.java:212)
	at cpw.mods.fml.common.LoadController.propogateStateMessage(LoadController.java:190)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:483)
	at com.google.common.eventbus.EventSubscriber.handleEvent(EventSubscriber.java:74)
	at com.google.common.eventbus.SynchronizedEventSubscriber.handleEvent(SynchronizedEventSubscriber.java:47)
	at com.google.common.eventbus.EventBus.dispatch(EventBus.java:322)
	at com.google.common.eventbus.EventBus.dispatchQueuedEvents(EventBus.java:304)
	at com.google.common.eventbus.EventBus.post(EventBus.java:275)
	at cpw.mods.fml.common.LoadController.distributeStateMessage(LoadController.java:119)
	at cpw.mods.fml.common.Loader.loadMods(Loader.java:513)
	at cpw.mods.fml.client.FMLClientHandler.beginMinecraftLoading(FMLClientHandler.java:208)
	at net.minecraft.client.Minecraft.func_71384_a(Minecraft.java:480)
	at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:878)
	at net.minecraft.client.main.Main.main(SourceFile:148)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:483)
	at net.minecraft.launchwrapper.Launch.launch(Launch.java:135)
	at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
Caused by: java.lang.ClassNotFoundException: net.minecraft.command.ICommand
	at java.net.URLClassLoader$1.run(URLClassLoader.java:372)
	at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(URLClassLoader.java:360)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
	... 35 more

Could someone tell me whats wrong?