The clear slider on one of our screen doors is sticking something awful. It wont slide back so we can reach/open the latch to go in or out. We have to give it a good rap to move it back. There is nothing in the track (we thought maybe a dead bug or twig) and it's not cocking. I oiled the track but the problem remains. What could be causing this? We can't see anything that can be causing this sticking.