Uhh...[SEVERE] stuff

[MoosyDoosy]

I've been getting quite the lag increase lately from my normally okay experience, so I've been trying to track down the source of the lag. It seems like it started ever since I've seen the following lines be spammed into my FTB log. Anyone know what it's saying?. Also, which mods in the Direwolf20 pack tend to cause the most lag? Another question: Which chunk loader would be the least laggy in general? As a note, the lag seems to increase whenever I open my inventory. Thank you.
2014-02-05 20:46:05 [INFO] [STDERR] java.util.ConcurrentModificationException
2014-02-05 20:46:05 [INFO] [STDERR] at java.util.HashMap$HashIterator.nextEntry(HashMap.java:894)
2014-02-05 20:46:05 [INFO] [STDERR] at java.util.HashMap$ValueIterator.next(HashMap.java:922)
2014-02-05 20:46:05 [INFO] [STDERR] at net.minecraft.nbt.NBTTagCompound.func_74734_a(SourceFile:25)
2014-02-05 20:46:05 [INFO] [STDERR] at net.minecraft.nbt.NBTBase.func_74731_a(SourceFile:119)
2014-02-05 20:46:05 [INFO] [STDERR] at net.minecraft.nbt.CompressedStreamTools.func_74800_a(CompressedStreamTools.java:140)
2014-02-05 20:46:05 [INFO] [STDERR] at net.minecraft.world.chunk.storage.AnvilChunkLoader.func_75821_a(AnvilChunkLoader.java:198)
2014-02-05 20:46:05 [INFO] [STDERR] at net.minecraft.world.chunk.storage.AnvilChunkLoader.func_75814_c(AnvilChunkLoader.java:184)
2014-02-05 20:46:05 [INFO] [STDERR] at net.minecraft.world.storage.ThreadedFileIOBase.func_75736_b(SourceFile:30)
2014-02-05 20:46:05 [INFO] [STDERR] at net.minecraft.world.storage.ThreadedFileIOBase.run(SourceFile:23)
2014-02-05 20:46:05 [INFO] [STDERR] at java.lang.Thread.run(Thread.java:724)

 

[UniZero]

I have had a similar error 3 times myself and the modpack guys know and are working on it. Be safe and take regular backups if you don't potentially want to lose your world.

 

[MoosyDoosy]

I have had a similar error 3 times myself and the modpack guys know and are working on it. Be safe and take regular backups if you don't potentially want to lose your world.

Yeah, but it's worrying because it gets spammed almost every two seconds whenever my inventory is opened so my log is just this error basically.