I don't own a Woz but I'd venture to say there's a optic switch behind that door that may not be seeing the ball so it keeps saying it is trying to locate ball. That may need to be cleaned or cleaned and adjusted.

Welcome and congratulations on owning a fantastic game. There are two tests I would suggest you run (if you don't know how to get into the test menu see page B-2 of the owner's manual), first with the ball behind the door go into switch tests and make sure that switch (it's a mechanical switch, not an opto) is registering when the ball is locked. If it's not then you'll probably need to bend the arm a little and make sure it's not mis-aligned or binding on the playfield. If that's working properly go into the coil test and run the test on 57 which is the single door motor. If it's loose on the post or it's binding on something you'll probably have to remove the castle mini playfield to adjust / tighten it, this looks daunting but it's not that bad if you follow the process in the manual.

Most likely the ball is not activating the switch behind the door. The machine does not realize there is a ball there. Like mentioned before, you need to go into your switch tests and see if the switch is being activated when a ball is behind the door. It is a simple adjustment to the switch. I will also note that I had to install some foam on mine in order to ensure the ball always sits in the correct spot (i.e. activating the switch).