Using Hats 2.1.1 I got the following error while flying around in Twilight Forest:

java.util.ConcurrentModificationException
at java.util.WeakHashMap$HashIterator.nextEntry(Unknown Source)
at java.util.WeakHashMap$EntryIterator.next(Unknown Source)
at java.util.WeakHashMap$EntryIterator.next(Unknown Source)
at hats.common.core.TickHandlerServer.serverTick(TickHandlerServer.java:127)
at hats.common.core.TickHandlerServer.tickEnd(TickHandlerServer.java:56)
at cpw.mods.fml.common.SingleIntervalHandler.tickEnd(SingleIntervalHandler.java:34)
at cpw.mods.fml.common.FMLCommonHandler.tickEnd(FMLCommonHandler.java:141)
at cpw.mods.fml.common.FMLCommonHandler.onPostServerTick(FMLCommonHandler.java:274)
at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:622)
at net.minecraft.server.integrated.IntegratedServer.func_71217_p(IntegratedServer.java:129)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:484)
at net.minecraft.server.ThreadMinecraftServer.run(SourceFile:583)

Not sure if this is Hats related or not but it was the only mod mentioned in the exception while none of the mods were flagged as errored by FML.

ForgeModLoader-client-0.log: http://paste2.org/xgPYBy5X
Crash Report: http://paste2.org/VyMO441W

have the same crash in overworld happens randomly

Same issue. Happened several times within 15 minutes killing blazes with Tinker's Construct Cleavers in Autonomous Activators.

http://pastebin.com/0ady4muh

3bca624

thanks hope this fixes it

Same error as here: #77