Audio Systems: 99 VW CD Changer error, vw new beetle, new beetle

Question
Hi, I have a 1999 VW New Beetle, and I have installed a USA Spec 6-CD changer in it.  The changer is connected in the trunk (left side) and I know it has power because when the magazine is inserted, it "cycles" through each CD.  The problem is that when I press the CD button on the dash, it says "no changer".  Any ideas?  Thanks so much!

Answer
This would all depend on the headunit and the interface to the changer that is used.
The changer should specify how to do this properly in its' installation/owners manual.
I have no idea if this is a tuner interface, a direct component or what. Therefore, I cannot help much more.
However, no matter what the interface uses, the manuals should specify how to emplement it.