I'm also having problems changing the address on my (new) Bachmann GP7.

I have an MRC Wireless system and have never had a problem before changing the address of any locomotive in my fleet including 3 other Bachmann's that were purchased previously.

This GP7 refuses to have its address changed.

Here are the steps I'm going through:
1. I'm attempting to reprogram it on my programming track (just like all my other locos).
2. I'm attempting to change it from "3" to "5608" which is the number on the cab.
3. The headlight changes in lighting intensity as I input values... So I know the decoder is receiving some sort of signal.
4. I take the loco off the programming track, put it on the main, punch in 5608 and nada.  I punch in 3 and all is good.  Argh!

I've also tried reprogramming it through the CV's and that does squat too.

I may be forced to call Bachamm service...