Do not unscrew that screw!
The correct technique on a Swiss watch is to pull the stem into the hand setting position, then a few turns (one or two turns) to loosen the grip of the retaining clip, then push down on the screw while gently pulling stem out. If it still does not release anothe
full turn on the screw to loosen some more.
If you unscrew that screw fully, you will have to remove the hands, the dial, then realign the release mechanism under the dial and reinsert the screw.
On some newer watches that screw is a push piece.
Geoff
Look at diagram on this url:
http://forums.watchuseek.com/f6/need-know-how-remove-stem-accutron-218d-156159.html