Well it happened, my "practice" mod file wont open in the tool set. I get wierd error message and have to reboot every time I try to open it.

The moral of the story...If your making a mod, back-up often because something causes certain files to go bad! ( I read that complex conversation strings do it, but my mod that went bad had none)

Well the good news is that Bioware is supposed to release a fix for this in the next week or so, but it probably wont be retroactive. :(
See the Bioware forums for more details.