This happens on my server either on world spawn or shortly after (whenever fire spawns in the world, i think)

http://pastebin.com/bhsqqG9H

Everything is up to date and single player works fine

Looks like a CodeChickenCore bug.
Possibly due to this file: assets/codechickencore/asm/tweaks.asm and its related commit: 9e43609
but I have no evidence myself.

Yeah, I screwed up, redownload your CCC