your door handles throw is not meeting up with the hole in the side of the door frame. In other words the hole that the throw fits into has slipped to one side or the other or most likely the wall or frame has shifted causing the lock not to meet up.
Close the door and with a flashlight see where the throw should be and then move the recepticle around to find where it lines up and then screw it back in.
Not a real problem, your home has shifted. Do this all the time.