Before you go traipsing off to a dealer, check to make sure that one of the black trim panels on the inside edges of the glass haven't detached themselves and thus block the way of the sunroof coming down.

This has happened several times on my '94. At first I would snap them back in place (they just snap in), but I finally just gave up. All they do is make it so you don't see the tracks from the inside, and I'd rather have a consistently working sunroof than no-see-um tracks.

If your dealer is nice, the service writer will probably check this issue first to make sure that's not the problem. But if you can check for it and save yourself the inconvenience, so much the better!