Many door knob and lockset problems can be corrected before they become so serious that you get locked out or the lock does not work at all. Often, a broken door latch assembly or door lock mechanism causes the problem.Sometimes a door lock mechanism may not work simply because it’s dirty or needs to be lubricated with graphite (do not use any type of oil because this will gum-up the works). An improperly functioning door latch may be the result of a poorly fitting door.