Strange one - Slots Missing

This is a strange one..

I've got 3 CDPCX300's hooked up, one per S-Link port on the S-linke.. So far so good, works like a champ - jumping from one player to another.

I programmed my Denon AVR5700 to change inputs thru event maps.

Here's the question.

Sometimes, on startup, a player will start searching for a disc in, say, slot 4. Doesn't find one, so goes to slot 5 and so on. Mind you that nothing has changed with the player - same CDs in the same slots.

Now, CDJ seems to be missing the slot completely. If I do a "complete/tedious" search of slots 1-10 (say 4 & 5 are missing), it looks at 1,2,3,6,7,8,9,10. Looks like 4 and 5 aren't even there.

This has happened twice..

Ideas?

PS - I unplugged everything, but nothing has changed...

Thanks for any help you can give!