Description: Exception in server tick loop

java.util.ConcurrentModificationException
	at java.util.HashMap$HashIterator.nextNode(HashMap.java:1429)
	at java.util.HashMap$KeyIterator.next(HashMap.java:1453)
	at net.minecraft.entity.EntityTracker.func_72788_a(EntityTracker.java:271)
	at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:967)
	at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:423)
	at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:798)
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:658)
	at java.lang.Thread.run(Thread.java:745