http://pastebin.com/qJSSzjqG

Player encountered this on my server, there is a good chance it is related to this mod.

Where did it happened? On server, or client?

Server.

Oh it should be client because there is Minecraft.class

Oh, does it happened from dedicated server side? It seems impossible.

It happened on a dedicated server, the player attempted to use the erebus dimension, and after I tried to deal with a ticking entity error, this error appeared.

The server is using KCauldron, as there aren't enough Forge mods to allow for all of the functions bukkit plugin allow.

Only this player crashes, so, clientside.

Is the crash report from the client, or from the server?... I think is what he's asking.

The player gave you that crash report?

Okay, id fix it till tomorrow.

Yes, the player gave me the crash report.

Fixed on commit: 19ee025

Fixed on efc1480.

I think your solution might be trying to load something on an invalid end of the game (occurs in servers only):

http://pastebin.com/gV00aVur