1997 mercedes 500s series CD changer problem code C 4 ERR?

Disconnected Battery for terminal cleaning & charging. Now, pwr antenna will not operate, Alpine 6 CD changer makes clicking sound, like trying to load CD's. Radio Display reads C-4 ERR. disconected CD changer,ck all fuses, under hood & in trunk. all grnds good. Cleaned terminals on amp with CRC elec contact cleaner.ck conect at antenna top & bottom black box. Can radio operate without CD changer connected? How To clear & what is Code displayed on radio?