If this is an interior door that 'hides' in the wall, it's called a Pocket Door. If it continually gets stuck, you need to do an inspection.
Can you run your fingers along the tracking and feel any dirt/grime? If so, clean it off. If you gently lift the door, spin the wheels to feel for 'flat spots'. If there are flat spots, the wheel(s) needs replacing. Maybe the door, itself, is damaged. Do you see any scraping on the door itself? Have you recently hung a picture or something along the 36" 'pocket'??? If so, the nail marks on the door are from the 'thing' you hung on the wall of the 'pocket'!
My best to ya and hope this helps. Let us know what you find out.