Is your boot damp. mine used to play up, sometimes would lock up for days or say disc error and sometimes would not even eject. this was caused by the boot leaking on the boot seal, only a small dribble but use to slowly fill the spare wheel hole up over time. just put a new boot seal on £50 from main dealer dried the boot out and took cd player indoors in the warm for a couple of days and now it seems to be ok. only ever done it once since when it was realy cold in the middle of winter. They just dont like the cold and damp.
hope this helps
Rob