java.util.ConcurrentModificationException
	at java.util.HashMap$HashIterator.nextNode(HashMap.java:1429)
	at java.util.HashMap$ValueIterator.next(HashMap.java:1458)
	at net.minecraft.world.chunk.Chunk.func_76623_d(Chunk.java:1032)
	at net.minecraft.world.gen.ChunkProviderServer.func_73156_b(ChunkProviderServer.java:484)
	at net.minecraft.world.WorldServer.func_72835_b(WorldServer.java:256)
	at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:920)
	at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:430)
	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)