Hmm, ok, well not sure what's going on, but you don't have to re-add it back to big.lab, you can just copy it into the root of your TPM directory (wherever wmain.exe is).
For some reason, we left in the code that would override the big.lab version if a same-name version exists in the root directory. Not sure if that is the reason you're getting an assert handler error, in fact I doubt it. What version of Windows are you running?
I'm not even certain that the sithjedi.baf doesn't contain some specialized code that the program recognizes, and tries to apply it to the player module, which causes the error...I'll look into it further.