I see you have looked in the Stilo section already but from the description you have given it does sound like a problem with the CD part of the set. If you haven't already tried this you might want to run a CD cleaning disc just in case it is a dirt laser lens and without wanting to sound like I'm teaching someone how to suck eggs, are you putting the disc in correctly, i.e. not upside down.
I don't know if you have had the car ages, in which case you obviously know which is the correct orientation but this is just in case the car/CD is new to you. I know on my first B&O Hi Fi just after CDs were invented, the CD mechanism was purchased from Aiwa and the disc had to be inserted label side down.
You could also check out the I.C.E section (see link below) although the topics are more likely to be generic as opposed to model specific.