2011-02-08 20:46:03 [SEVERE] Unable to spawn mob. Error:
java.lang.ClassNotFoundException: net.minecraft.server.EntityZombieSimple
        at java.net.URLClassLoader$1.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at org.bukkit.xmlns.spawnmob.Mob.spawn(Mob.java:77)
        at org.bukkit.xmlns.spawnmob.SMPlayerListener.onPlayerCommand(SMPlayerLi
stener.java:51)
        at org.bukkit.plugin.java.JavaPluginLoader$3.execute(JavaPluginLoader.ja
va:133)
        at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.jav
a:60)
        at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.j
ava:213)
        at net.minecraft.server.NetServerHandler.c(NetServerHandler.java:590)
        at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:563)
        at net.minecraft.server.Packet3Chat.a(SourceFile:24)
        at net.minecraft.server.NetworkManager.a(SourceFile:232)
        at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:71)
        at net.minecraft.server.NetworkListenThread.a(SourceFile:104)
        at net.minecraft.server.MinecraftServer.h(MinecraftServer.java:283)
        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:209)
        at net.minecraft.server.ThreadServerApplication.run(SourceFile:512)