Crash upon adding new JAR

I'm getting this error:

[SEVERE] Encountered an unexpected exception ClassCastException
java.lang.ClassCastException: com.bergerkiller.bukkit.nolagg.spawnlimiter.EntityWorldWatcher cannot be cast to net.minecraft.server.WorldManager
at net.minecraft.server.World.makeSound(World.java:769)
at net.minecraft.server.Entity.z(Entity.java:254)
at net.minecraft.server.EntityLiving.z(EntityLiving.java:263)
at net.minecraft.server.Entity.h_(Entity.java:216)
at net.minecraft.server.EntityLiving.h_(EntityLiving.java:435)
at net.minecraft.server.World.entityJoinedWorld(World.java:1245)
at net.minecraft.server.WorldServer.entityJoinedWorld(WorldServer.java:511)
at net.minecraft.server.World.playerJoinedWorld(World.java:1227)
at net.minecraft.server.World.tickEntities(World.java:1125)
at net.minecraft.server.WorldServer.tickEntities(WorldServer.java:428)
at net.minecraft.server.MinecraftServer.q(MinecraftServer.java:563)
at net.minecraft.server.DedicatedServer.q(DedicatedServer.java:213)
at net.minecraft.server.MinecraftServer.p(MinecraftServer.java:473)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:405)
at net.minecraft.server.ThreadServerApplication.run(SourceFile:539)

This seems to be happening every time I start it up. I'm running this off Crunchbang Linux, java 6, 2GB's of RAM. What's happening and how do I fix it?

 

can u post a list of your plugins?

 

It's NoLagg, refer to the response I made here for another user have the same issue.