There are small screws that hold the door on...there is a small amount of adjustment there, so make sure the screws are both there and tight. Also look to see if you are binding up on the wire rail just outside that door....sometimes the hinge side of the door hits that rail and you end up having to put a very slight outward bend in that rail to keep that from happening.
I am basing this on you saying that it works during game play...which would indicate the switches are fine. One other thing to look at...make sure one of your balls is not magnetized and sticking to the door post. This happens a lot with some brand of balls, especially in games full of magnets like WOZ.