Actually enterprise12's crash is presumably caused by a faulty mod (threaded world access), run with -Dfastcraft.debug.fwel (startup option, goes before -jar) to try catching it.
This is also on client side only, i didnt add it server side.
Could you please look at this, i discussed this crash with the authors of Mekanism and CoFH, because removing fastcraft when getting the error i stated, makes a different one.
Perhaps you may know something they dont.
Here is the link to the discussion:
Hopefully you can all somehow fix this issue, because my players crash