Coding a replacement CD Changer - Nissan X Trail?

I purchased a used, replacement CD Changer for my 2002 X Trail (Nissan Part No. 28184-4M500; Clarion Model PN-2302M). When I connected it (ignition off) all CD lights flashed red and the unit beeped continuoisly. Questioned supplier who said it needs to be coded to the vehicle at a Nissan dealer. 2 dealers locally were not aware of this. Radio coding, yes, after battery disconnection. Anybody experienced this problem?