Update any mods that have the IC2 API. if the problem still happens, go into the mods and delete the IC2 folder in them. if it still happens, then I have no clue.
I am sorry to be ignorant, but how would I be able to determine WHICH of my mods have IC2 API? I am so sad.. this is my FAVORITE mod, and it killed my oldest and most developed world... heh ahh!!!!