As a note, I am not getting this on a fresh install, about to start the process of finding what mod is causing this interaction, will update when found.

Crash Report: http://pastebin.com/fminpytN

EDIT: After testing, I was able to quickly determine that the offending mod was Redstone Armory from Team CoFH,

Yeah, that's due to the way ic2 packages their api. If you don't want to remove RA you can just install the latest ic2api jar from their Jenkins and it should fix the issue