Description: Exception in server tick loop

java.util.ConcurrentModificationException
	at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:819)
	at java.util.ArrayList$Itr.next(ArrayList.java:791)
	at net.minecraft.server.v1_4_R1.EntityTrackerEntry.track(EntityTrackerEntry.java:85)
	at net.minecraft.server.v1_4_R1.EntityTracker.updatePlayers(EntityTracker.java:138)
	at net.minecraft.server.v1_4_R1.MinecraftServer.r(MinecraftServer.java:589)
	at net.minecraft.server.v1_4_R1.DedicatedServer.r(DedicatedServer.java:224)
	at net.minecraft.server.v1_4_R1.MinecraftServer.q(MinecraftServer.java:494)
	at net.minecraft.server.v1_4_R1.MinecraftServer.run(MinecraftServer.java:427)
	at net.minecraft.server.v1_4_R1.ThreadServerApplication.run(SourceFile:849)