Errrr... I thought that was what I said?
Crown unscrewed from the tube = runs fine
Crown screwed down to the tube = stops
If that's the symptom, it sounds like the stem is too long, and is binding or pressing against something (maybe the wheel for the center seconds)?
For what it's worth... I've always re-used the same stem as originally came with my watch when swapping crowns/tubes, and haven't had any issues to date. It's possible, however, that the tube you have is too short... I had this problem on one of my old MBW's. I shortened the stem up by a thread or two, and it was just right afterwards...