6 disc cd changer jammed in 2004 mercury mountaineer, says error when i try to eject or play jammed discs.

If one of the discs slipped off its tray and got jammed, you will have to take the cd changer out of the car and dislodge the jammed cd.
I had this happen a few years back and the guys at the auto parts store helped me remove it for free.

If u can access it you could pull it out with needlenose pliers if not it might need to be removed good luck hope this helps

fuel filter

The CD laser is dirty. Use a CD cleaner disc first, before replacing
the head unit. Good luck.

My endeavor has done this error 3 a couple of times and the cd changer basically shuts off all lights and won't do anything. Someone on another solution page said to slide a credit card back and forth in the cd opening to fix the problem. I've done this both times and it has made the changer play again as if nothing had happened : )

sorry unit is not servicable you can get a used one at many junkyards

I have the same problem with the 2006 sentra

I had the same problem for months. I checked the owners manual, checked the fuse box, everything I could think of. Then, today, I did some online research and someone said one of the CD's is probably just jammed or slipped out a bit. The suggestion was to gently slide a credit card over the disk (through the door/slot, which in my case was partially open). I just tried it. The door closed and the message said "initializing". It worked! The CD player is back to normal.

One common solution is to disconnect the negative battery cable for 10minutes. When you reconnect, the stereo should reset itself and allow you to eject your CD's . Best of luck!
Greg

had to replace player twice, luckily it was under warranty. FACTORY PLAYER JAMS EASILY !!! What I have learned is to put cd player in radio mode before ejecting instead skipping form disc to disc.