java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.remove(Unknown Source)
at net.minecraft.world.gen.ChunkProviderServer.tick(ChunkProviderServer.java:262)
at net.minecraft.world.WorldServer.tick(WorldServer.java:207)
at net.minecraft.server.MinecraftServer.updateTimeLightAndEntities(MinecraftServer.java:756)
at net.minecraft.server.MinecraftServer.tick(MinecraftServer.java:668)
at net.minecraft.server.integrated.IntegratedServer.tick(IntegratedServer.java:252)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:526)
at java.lang.Thread.run(Unknown Source)