Try this, empty cd changer, put it back in, see if it finds cd1 the one that's stuck in there, if not tap the cd changer with something hard like the handle of a scrapper, this will jolt the player & possible allow the cd to jump back into the cassette drawer, if you can get the player or the cassette to find the cd u can get it back, if u know for sure what number the lost cd was in ie what drawer it was in, 1 is at the bottom, then fill the other drawers with cds, but not that drawer and allow them to play for a second or 2, if all of them play & the empty 1 doesn't that's the slot with the stuck cd in it, eject the cassette, & put it straight back in, it will automatically open drawer 1 as it does so bang the cassette with the plastic several times, again hopefully this jolting will get the cd to jump back into the drawer, if you have 2 cds in the same slot only 1 can get out but if u leave that slot empty there is a chance u can shock it back, otherwise its take it out take of lid & remove it that way, also get a torch look into the changer with cassette out & see if u can see the cd u may be able to get it out gently with a curved set of surgical pliers the type fishermen use for getting out hooks.

Also banging the cassette whilst pressing the eject button will release a stuck cassette when code CDDJ Error is up, once cassette is out take out all the cds, put in just 4 fresh ones, turn radio system off & car completely, turn it back on & reinsert changer, if its making noises its probably working again, check to see if its accepted a cd & playing, if the code is still showing turn everything off & back on again, it should be working showin 4 cds that are full & 2 empty. if none of this makes ur 6 stack work or eject then its b*****ed, I sorted a few this way.