How can I correct the "Error" code displayed on my Sony 6CD?

I have a 2005 (55 plate) Ford Mondeo TDCi, Ghia with a Sony Radio/CD:-
Unit Type SOCD 6N, Serial No. Moo6324.
The radio seems fine but the CD will not operate with the screen displaying "Error". I cannot load or unload the 6 CD's.
The FordService Audio Guide handbook for this fault message advises visiting "Ford Main Dealership".
Can anyone offer any help or guidance? Thanks