Had a similar problem a month ago. There is a cable that is routed over a plasitc wheel on both the top and bottom of the window rail. It is possible,as in my situation, that the cable came off one of the guide wheels. Im my case, it slipped behind the wheel and was lodged between the wheel and the metal window rail. The motor still moves the cable, but with much more resistance, and thinks there is an obstruction, which forces the window to open. There is very little play in the cable and I could not get mine back on the wheel without disconnecting the cable. Still cannot figure out how to get it back together and take up the slack after it is reconnected.
Hope you have better luck with yours. I had to disconnect the whole thing and prop the window up. My cable kinked badly and broke off a plasitic retainer in the motor. I am still deciding what to do with mine. If you come up with any instructions or ideas on how to reconnect the whole thing, please post. I would love to get my window back. There has to be a way to reconnect the cable and take up the slack.