CurrentModificationException

[svdragster]

2013-10-26 22:32:43 [SEVERE] Encountered an unexpected exception ConcurrentModificationException
java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextEntry(HashMap.java:894)
at java.util.HashMap$KeyIterator.next(HashMap.java:928)
at net.minecraft.server.EntityTracker.a(EntityTracker.java:195)
at net.minecraft.server.MinecraftServer.t(MinecraftServer.java:515)
at net.minecraft.server.DedicatedServer.t(DedicatedServer.java:204)
at net.minecraft.server.MinecraftServer.s(MinecraftServer.java:432)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:361)
at net.minecraft.server.ThreadMinecraftServer.run(ThreadMinecraftServer.java:13)
2013-10-26 22:32:43 [INFO] Stopping server
2013-10-26 22:32:43 [WARNING] [CanaryMod] Server Listening Thread inturrupted
2013-10-26 22:32:43 [INFO] Closing listening thread
2013-10-26 22:32:43 [INFO] Saving players

As you see at the bottom it stops the server. I was playing with some people on my server and we were killing alot of mobs, like hundreds. It just randomly appeared multiple times and stopped the server.

[darkdiplomat]

There is not really enough information here to really define what the root cause of the problem is.
A Current Modification Exception typically occurs in an instance where two or more threads are attempting to read and modify a collection. With out exactly knowing what is attempting to do such things, i can't address the issue fully or properly.