Its a long time since I had one to bits, but 2 things seem to lead to jamming, the 1st is the front of the sliding roof jamming on the wind deflector, because the pivot points on the retracting struts have corroded, this is easy to spot.
However not so easy to spot is the problem I think you have! removing the sliding roof panel is a matter of a few screws etc, and carefully lifting away from the car, this will reveal the the 2 brackets (O/S and N/S) that give the S/R its drive, these brackets are attached to the winding cable. Expose the cables by removing the cable covers that run either side of the S/R aperture, and you'll find that one side or the other, the bracket has become detached from the cable... if this is the case, you will need to source a new cable.
Thom