After the 3rd EER3 code I took the darn CD changer apart.
It has thin white plastic gears that shift the 6 disk holder up & down. When these gears get worn out the disk holder jams in a binding position. Some are lucky to have the changer get jolted back into correct position but once those gears get worn/damaged it will bind again.
I gave up and found a Pioneer 6 changer that fit in the same spot but also had to change out the head unit to be compatible.