Chris,
What kind of door is it (metal, wood, fiberglass)? Does it have slinky type springs, or a windup spring? If it has a wind up spring, do NOT fool with it - they are for pros only.
Over time, the tracks go out of alignment, the grease on the rails gums up, and the rollers seize or become dirty. Lubricate everything well, clean and re-align your sensors, and check your spring tension (if you have the slinky springs).
Bill
215g FOWLR... and anemones, GSP, gorgonians... carp, that isn't FO!
"I killed my first SW Fish in 1971..."