Same thing happened to my passenger window last summer, it would get stuck if I rolled it all the way down. I didn't have time to screw around with it and since I ride in mine by myself 99.9% of the time, I rolled it up and disconnected the power connection...lol!!

__________________
2002 X5 4.6is
1999 C5 Corvette
1992 Mitsubishi 3000GT VR-4
1994 Kawasaki ZX-9R
2005 Mazda 6 Wagon (Wife's)
1991 Mitsubishi 3000GT VR-4