kept error

2012-07-10 19:33:04 [INFO] Creating empty config: /games/ni74159_1/ftproot/minecraftbukkit/plugins/Essentials/userdata/otffina.yml
2012-07-10 19:33:04 [INFO] otFFina [/46.109.140.34:1250] logged in with entity id 1315319 at ([world] -239.5, 94.62000000476837, 303.5)
2012-07-10 19:33:04 [SEVERE] Could not pass event PlayerJoinEvent to AuthMe
org.bukkit.event.EventException
	at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:304)
	at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62)
	at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:460)
	at net.minecraft.server.ServerConfigurationManager.c(ServerConfigurationManager.java:132)
	at net.minecraft.server.NetLoginHandler.b(NetLoginHandler.java:129)
	at net.minecraft.server.NetLoginHandler.a(NetLoginHandler.java:94)
	at net.minecraft.server.Packet1Login.handle(SourceFile:68)
	at net.minecraft.server.NetworkManager.b(NetworkManager.java:229)
	at net.minecraft.server.NetLoginHandler.a(NetLoginHandler.java:48)
	at net.minecraft.server.NetworkListenThread.a(NetworkListenThread.java:61)
	at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:567)
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:459)
	at net.minecraft.server.ThreadServerApplication.run(SourceFile:492)
Caused by: java.lang.NoClassDefFoundError: net/milkbowl/vault/permission/Permission
	at uk.org.whoami.authme.Utils.setGroup(Utils.java:33)
	at uk.org.whoami.authme.listener.AuthMePlayerListener.onPlayerJoin(AuthMePlayerListener.java:429)
	at sun.reflect.GeneratedMethodAccessor134.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.lang.reflect.Method.invoke(Unknown Source)
	at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:302)
	... 12 more
2012-07-10 19:33:17 [INFO] [AuthMe] otFFina§f registered 46.109.140.34