This is what I did to my In-Dash 6 disc CD Player in my Ford.
Rather that toss the radio like most are saying to do
you can try this first.
Pull the radio out and remove the screw on each side and the 2 on the back. Pop off the cover and you can see the CD's. The part of the CD changer may have not fully engaged the CD it wanted to play and it is stuck not knowing what to do. Press on the CD that so that the part that spins the CD is locked into the center of the CD. Leave the top open and plug in the CD player. It should start going through all of the cd's then if the CD error is gone it will play again.
Mine works fine now.