CaveSquid

SOLUTION: I experienced the same problem tonight. And found the solution. Apparently Steam must have indeed updated the game tonight (I have it set on Auto), and this in turn seems to have broken some of the mods. Try disabling some of the mods in your DATA folder until you can pin-point which one(s) broke.. This did the trick for me. In my case it turned out to be Val's Crafting Meltdown Alpha mod (version 1.5a with arrow crafting ~the one without arrows will still work though).