Ok, I had a barrel (Factorization) hooked up to some itemducts (Thermal Expansion), and picked up the barrel with a Gravity Gun (GraviGun mod). The game then crashed with an "ArrayIndexOutOfBoundsException" error, and does the same every time I try to open that world.
I have no idea what happened and would appreciate any help with recovering that saveworld. I wasn't sure where to post this because I have a ton of mods installed, so I figured, "Those Forge folks are pretty smart!" and so here I am.
Also, the attachment thing doesn't seem to work for me, so I put my logfile on MediaFire. https://www.mediafire.com/?5jiqqnckob7rkw0