My Twilight zone has recently started to develop a phantom lock. I will be playing a ball or sometimes waiting to shoot a ball with the ball in the shooter lane and it will say that a ball was just locked.

I checked the Cherry switch for the lock out hole and it seemed fine. I also removed all four opto sensors and cleaned them with a q-tip and rubbing alcohol. I thought I had the problem fixed until a few games afterward it started doing it again.

Has anyone experienced this or know what I can do to try and diagnose the cause?

Good thought! I checked the eject plunger, it operates smoothly, and does not interfere or get hung up on the playfield.

Any ideas on what to check next?

Ok, I'll take a look at it during gameplay when it happens.

I took a look at the opto board as you suggested and all of the solder joints look okay. I think that is a good idea to post up over in the Twilight zone owners thread; I will do that now.