I'd change CV29 to value of 2 and leave it their. This turns analog conversion off. Known cause of few issues.
To change the 2 digit address you must be on the programming track, OPS will not work. Other suggestion if this does not work, reset to defaults.
http://www.tracksidesales.com/decoder_reset.htm
This will bring it back to 2 digit default address 3. Best of luck
---
You might want to try putting the Zephyr into "blast mode" for programming by changing OPSSW #7 to closed (C). Be aware you must remove the connection to layout and only leave the program track connected. Blast mode sends the commands out on program track AND rail A rail B from what I've read. Change the OPSSW $7 back to thrown (T) when finished. This is not documented in the book but came up in Digitrax forum and JMRI forum.
,but with the two 'ts
I asked the same thing about a month ago. No problem after I finally paid attention to the instructions I had been flipping past for almost a year in my decoder manuals.
What address are you trying to enter, 2 digit or 4 digit ?
2 digit can only be changed/set on the program track.
4 digit can be changed/set on the main (OPS).
You must change CV29 to permit 4 digit addressing. Put 34 as a value in CV29 if you want 4 digit address. Put a value of 2 in CV29 if you want 2 digit addressing.
Do you have DecoderPro at home ?