Driver window won't close

Had a weird problem today where I tried to put up my window in my SW20 and it just stopped halfway up and wouldn't go up any further with the switch. When I pull it up with my hands and close the door it slides down a little. I don't believe it's an electrical fault as it goes down fine and if it's at the bottom will go up if pressed, but as said, will stop halfway. Any ideas what could cause this and what the fix would be? Thanks heaps.