Hi I got this of the E30zone.net it might help a bit.
One of the cables has jumped on the main drive sprocket on the motor.
Unscrew the three bolts that hold the motor assembly in place and drop the motor down. With luck you may be able to re-time the roof by moving the cables along with a screwdriver, or get the roof into the positions it needs to be in to remove the steel panel.
Still leaves the problem of what went wrong in the first place, of course. You may have damaged one of the cables and/or the drive sprocket.