Quoted from Captive_Ball:
Is it the ball lock area shown below? Are you able to get 3 balls locked there to start the Multiball? Hopefully the post releases them when multiball starts and/or when the game is complete. If you start a game right away after completing one and there are balls in the lock, it will not release them.
When I first got my BM66 (second owner) the ball lock would sometimes not release. I seem to recall making a slight adjustment to its positioning from underneath and applying a very small amount of white grease to the plastic plunger (a little goes a long way which you don't want to clean up later).
Otherwise the ball is supposed to lock there after you hear the call out of "lock is lit", meaning you are now able to lock balls. After that you'll hear "ball 1 locked" etc until ball 3 at which you get a multiball. At the end of the game if you haven't reached multiball all the balls that have been locked should release before your next game.
I'm still confused as to where the ball is getting stuck behind the L catwoman ramp. What position is the rotating playfield in when this happens?