Here's my crash report:
http://openeye.openmods.info/crashes/2bbab11485ee6a0eb3e01507a789e5c5
I place an Electrolytic Separator and when I "use" it, it crashes.

Thanks in advanced.

This happens due to a bad interaction with ThermalExpansion which, according to KingLemming, was a vanilla bug. We haven't had any reports of it in 1.7 so assuming Mojang have fixed it now.