I was testing my mod, and singleplayer works just fine. But when starting a server, it gives:

 [sEVERE] Encountered an unexpected exception NoClassDefFoundError
java.lang.NoClassDefFoundError: ModName/ModelHuman

And the file is there, but it doesn't seem to find it.

 

Do I need to register a model first or?

 

This is the entire error log, if thats more helpfull.

 [iNFO] Starting minecraft server version 1.5.2
[sEVERE] Encountered an unexpected exception NoClassDefFoundError
java.lang.NoClassDefFoundError: dpmod3rdimpact/ModelHuman
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at cpw.mods.fml.common.ModClassLoader.loadBaseModClass(ModClassLoader.java:86)
at cpw.mods.fml.common.modloader.ModLoaderModContainer.constructMod(ModLoaderModContainer.java:483)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at com.google.common.eventbus.EventHandler.handleEvent(EventHandler.java:74)
at com.google.common.eventbus.SynchronizedEventHandler.handleEvent(SynchronizedEventHandler.java:45)
at com.google.common.eventbus.EventBus.dispatch(EventBus.java:314)
at com.google.common.eventbus.EventBus.dispatchQueuedEvents(EventBus.java:296)
at com.google.common.eventbus.EventBus.post(EventBus.java:267)
at cpw.mods.fml.common.LoadController.propogateStateMessage(LoadController.java:165)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at com.google.common.eventbus.EventHandler.handleEvent(EventHandler.java:74)
at com.google.common.eventbus.SynchronizedEventHandler.handleEvent(SynchronizedEventHandler.java:45)
at com.google.common.eventbus.EventBus.dispatch(EventBus.java:314)
at com.google.common.eventbus.EventBus.dispatchQueuedEvents(EventBus.java:296)
at com.google.common.eventbus.EventBus.post(EventBus.java:267)
at cpw.mods.fml.common.LoadController.distributeStateMessage(LoadController.java:98)
at cpw.mods.fml.common.Loader.loadMods(Loader.java:503)
at cpw.mods.fml.server.FMLServerHandler.beginServerLoading(FMLServerHandler.java:85)
at cpw.mods.fml.common.FMLCommonHandler.onServerStart(FMLCommonHandler.java:350)
at net.minecraft.server.dedicated.DedicatedServer.startServer(DedicatedServer.java:69)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:430)
at net.minecraft.server.ThreadMinecraftServer.run(ThreadMinecraftServer.java:16)
Caused by: java.lang.ClassNotFoundException: dpmod3rdimpact.ModelHuman
at cpw.mods.fml.relauncher.RelaunchClassLoader.findClass(RelaunchClassLoader.java:238)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
... 30 more
Caused by: java.lang.RuntimeException: Attempted to load class dpmod3rdimpact/ModelHuman for invalid side SERVER
at cpw.mods.fml.common.asm.transformers.SideTransformer.transform(SideTransformer.java:50)
at cpw.mods.fml.relauncher.RelaunchClassLoader.runTransformers(RelaunchClassLoader.java:352)
at cpw.mods.fml.relauncher.RelaunchClassLoader.findClass(RelaunchClassLoader.java:225)
... 32 more

make sure your model is in fact there, if not put it in the right location.