how can i fix my Clarion 6 cd multichanger?

Hi, i have a 6 cd multichanger which wont play. It comes up with error 6 which according to the manual is either a dirty or damaged disc, or the disc is in upside down. I have changed the disc for a couple of brandnew discs, and tried them in both ways, also i have cleaned the laser with no effect. It does everything but play ?? If anyone has any idea to what this could be i would be grateful for any feedback, many thanks, cj.