If it is at the bottom of the lock/handle side then the glass needs re-packing (toe & heeling) and/or hinges adjusting.
Mike at Agree-a-price frames
September 2010
It could be possible that the runner is damaged underneath, but they are adjustable, there should be a hole where you can insert a screwdriver at the corner, I had the same trouble so i took off the door and replaced the two runners
sean
July 2010
Automatic Answer
We may have found other answers which could help you.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix windows and doors.