A couple of friends and I created a server today, we played for about two hours and then from nowhere this error came up in the console: Code: 2011-08-15 15:14:53 [SEVERE] java.util.ConcurrentModificationException 2011-08-15 15:14:53 [SEVERE] at java.util.ArrayList$Itr.checkForComodification(Unknown Source) 2011-08-15 15:14:53 [SEVERE] at java.util.ArrayList$Itr.next(Unknown Source) 2011-08-15 15:14:53 [SEVERE] at net.minecraft.server.ChunkLoader.a(SourceFile:121) 2011-08-15 15:14:53 [SEVERE] at net.minecraft.server.ChunkRegionLoader.a(SourceFile:62) 2011-08-15 15:14:53 [SEVERE] at net.minecraft.server.ChunkProviderServer.saveChunk(ChunkProviderServer.java:164) 2011-08-15 15:14:53 [SEVERE] at net.minecraft.server.ChunkProviderServer.saveChunks(ChunkProviderServer.java:213) 2011-08-15 15:14:53 [SEVERE] at net.minecraft.server.World.save(World.java:216) 2011-08-15 15:14:53 [SEVERE] at net.minecraft.server.World.doTick(World.java:1732) 2011-08-15 15:14:53 [SEVERE] at net.minecraft.server.MinecraftServer.h(MinecraftServer.java:444) 2011-08-15 15:14:53 [SEVERE] at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:363) 2011-08-15 15:14:53 [SEVERE] at net.minecraft.server.ThreadServerApplication.run(SourceFile:422) All clients whent down to about 0-2 fps and there was no way to play. I tried to use mc edit to remove all the new chunks that we didn't build anything in but it didn't work. I've also tried Chunkster but that didn't make any progress either. Anyone know what it can be? Help appreciated