Remove the sliding screen and inspect the top and bottom rollers. Remove and replace rollers that do not play smoothly with new ones from your local warehouse store. Your door may be too short and does not fit in the door frame. In this case, you should loosen the screws attaching the top and bottom rails, without taking them all the way out, and extend the length of the door by sliding the slots along the screw. Once you have increased the length enough to allow the door to fit properly, re-tighten the screws.