CD "No Disk" Message

I've got a '99 VDP that I purchased a few months ago. The CD player had been working fine. After replacing some CDs and putting the cartridge back in the player, at the front console, it scrolls through like it's checking for the disks, but after checking for the 6th disk, it comes up with a "No disk" or is it "No Disc" message. I've checked to ensure that all CDs are in the cartridge correct side up/down. I've used a different cartridge with the same results. Has a cable come loose? Got any clues? Couldn't find anything through archive searches; so, sorry if the answer is in there. THX ahead of time!

Did you use copied discs? Some multichangers can't handle them.