Whenever I try to use the 'help' command, I get an error stating 'An unknown error occurred while attempting to perform this command'.  I have been pruning the mods mentioned in the console when this error pops up, but I'm still getting this error, and now there doesn't seem to be any source that I can discern.

 

Console output

 

2014-01-12 15:45:57 [iNFO] [sTDERR] java.lang.IllegalArgumentException: Comparison method violates its general contract!

2014-01-12 15:45:57 [iNFO] [sTDERR] at java.util.ComparableTimSort.mergeLo(Unknown Source)

2014-01-12 15:45:57 [iNFO] [sTDERR] at java.util.ComparableTimSort.mergeAt(Unknown Source)

2014-01-12 15:45:57 [iNFO] [sTDERR] at java.util.ComparableTimSort.mergeCollapse(Unknown Source)

2014-01-12 15:45:57 [iNFO] [sTDERR] at java.util.ComparableTimSort.sort(Unknown Source)

2014-01-12 15:45:57 [iNFO] [sTDERR] at java.util.ComparableTimSort.sort(Unknown Source)

2014-01-12 15:45:57 [iNFO] [sTDERR] at java.util.Arrays.sort(Unknown Source)

2014-01-12 15:45:57 [iNFO] [sTDERR] at java.util.Collections.sort(Unknown Source)

2014-01-12 15:45:57 [iNFO] [sTDERR] at net.minecraft.command.CommandHelp.func_71534_d(SourceFile:74)

2014-01-12 15:45:57 [iNFO] [sTDERR] at net.minecraft.command.CommandHelp.func_71515_b(SourceFile:36)

2014-01-12 15:45:57 [iNFO] [sTDERR] at net.minecraft.command.CommandHandler.func_71556_a(CommandHandler.java:88)

2014-01-12 15:45:57 [iNFO] [sTDERR] at net.minecraft.network.NetServerHandler.func_72566_d(NetServerHandler.java:759)

2014-01-12 15:45:57 [iNFO] [sTDERR] at net.minecraft.network.NetServerHandler.func_72481_a(NetServerHandler.java:728)

2014-01-12 15:45:57 [iNFO] [sTDERR] at net.minecraft.network.packet.Packet3Chat.func_73279_a(SourceFile:49)

2014-01-12 15:45:57 [iNFO] [sTDERR] at net.minecraft.network.MemoryConnection.func_74428_b(MemoryConnection.java:89)

2014-01-12 15:45:57 [iNFO] [sTDERR] at net.minecraft.network.NetServerHandler.func_72570_d(NetServerHandler.java:141)

2014-01-12 15:45:57 [iNFO] [sTDERR] at net.minecraft.network.NetworkListenThread.func_71747_b(NetworkListenThread.java:54)

2014-01-12 15:45:57 [iNFO] [sTDERR] at net.minecraft.server.integrated.IntegratedServerListenThread.func_71747_b(IntegratedServerListenThread.java:109)

2014-01-12 15:45:57 [iNFO] [sTDERR] at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:691)

2014-01-12 15:45:57 [iNFO] [sTDERR] at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:587)

2014-01-12 15:45:57 [iNFO] [sTDERR] at net.minecraft.server.integrated.IntegratedServer.func_71217_p(IntegratedServer.java:129)

2014-01-12 15:45:57 [iNFO] [sTDERR] at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:484)

2014-01-12 15:45:57 [iNFO] [sTDERR] at net.minecraft.server.ThreadMinecraftServer.run(SourceFile:583)

2014-01-12 15:45:57 [iNFO] [Minecraft-Client] [CHAT] An unknown error occurred while attempting to perform this command

 

 

ForgeModLoader-client0.log dropbox link - https://dl.dropboxusercontent.com/u/19887338/ForgeModLoader-client-0.log

Use another version of Forge.

This is caused by one of the mods you have installed, messing up the sort function.

Try removing mods and see if you can track it down.

This is caused by one of the mods you have installed, messing up the sort function.

Try removing mods and see if you can track it down.

I was able to remove the offending mods over time, but the biggest issue I ran into was that it seemed to be inconsistent, like I would load up my world once and it would work, then when I loaded again I got the error. 

 

Is there any reason it would behave like this?

No clue, modders do weird things.