Problems with a 5-disc car cd changer.?

The car is a mercedes slk-320 2001. The system is the original mercedes bose. The cd changer is at the trunk. The problem is that the stereo won�t read the discs. It starts reading, and says NO CD1, NOCD2,....... and then MAGAZINE EMPTY. Ive tried with different cds and I dont know what the problem is.