Join error

011-04-06 12:30:10 [SEVERE] Could not pass event PLAYER_JOIN to Achievements
java.lang.LinkageError: loader constraint violation: loader (instance of org/bukkit/plugin/java/PluginClassLoader) previously initiated loading for a different type with name "com/nijiko/permissions/PermissionHandler"
	at com.nidefawl.Stats.Permissions.NijiPermissionsResolver.permission(NijiPermissionsResolver.java:39)
	at com.nidefawl.Achievements.Achievements.load(Achievements.java:332)
	at com.nidefawl.Achievements.Achievements$AchievementsListener.onPlayerJoin(Achievements.java:409)
	at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:169)
	at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:59)
	at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:255)
	at net.minecraft.server.ServerConfigurationManager.a(ServerConfigurationManager.java:98)
	at net.minecraft.server.NetLoginHandler.b(NetLoginHandler.java:87)
	at net.minecraft.server.NetLoginHandler.a(NetLoginHandler.java:27)
	at net.minecraft.server.NetworkListenThread.a(SourceFile:87)
	at net.minecraft.server.MinecraftServer.h(MinecraftServer.java:368)
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:283)
	at net.minecraft.server.ThreadServerApplication.run(SourceFile:375)
2011-04-06 12:30:10 [SEVERE] Could not pass event PLAYER_JOIN to Stats
java.lang.LinkageError: com/nijiko/permissions/PermissionHandler
	at com.nidefawl.Stats.Permissions.NijiPermissionsResolver.permission(NijiPermissionsResolver.java:39)
	at com.nidefawl.Stats.Stats.load(Stats.java:832)
	at com.nidefawl.Stats.StatsPlayerListener.onPlayerJoin(StatsPlayerListener.java:132)
	at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:169)
	at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:59)
	at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:255)
	at net.minecraft.server.ServerConfigurationManager.a(ServerConfigurationManager.java:98)
	at net.minecraft.server.NetLoginHandler.b(NetLoginHandler.java:87)
	at net.minecraft.server.NetLoginHandler.a(NetLoginHandler.java:27)
	at net.minecraft.server.NetworkListenThread.a(SourceFile:87)
	at net.minecraft.server.MinecraftServer.h(MinecraftServer.java:368)
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:283)
	at net.minecraft.server.ThreadServerApplication.run(SourceFile:375)