Probably the solonoid that releases the latch (or maybe even a wire disconnected. The inside of the door will probably have to be removed for checking it. The unit will have 2 terminals on it. With all power off, take off the wires going to it and connect a bulb and battery across the terminals. if the bulb lights the unit is OK and the fault is elswhere on the machine - if not, the unit is faulty and should be replaced.
Graeme, September 2005