As you can see, it has been a great deal of time since I originally posted this issue. I got extremely frustrated with the issue and walked away from my layout concentrating on other endeavors. One night I was laying in bed reviewing the issue and determined that I never really checked continuity in the Command wire. The next day I did in fact check the continuity of both sides of the command wire. Everything proved to be nominal. I decided that it would not be a big effort to change out the command wire just as a precaution. I removed the wire from the problem BPC and went to the barrier strip that distributes the data to all of my different control boxes. The first lug took the requisite amount of tork to loosen. The second lug was extremely easy to loosen. Could it be I wondered? Tightening down both lugs securely and reattaching the data wire to the troublesome box, I issued a command. It worked. How long that one screw terminal had not been tightened down adequately is anyone's quess. And why it abruptly started failing after year(s) of service is an electrical mystery. So now all is well again on the Elmira Branch.
Moral of the story: Make sure all your connections are adequately torked. I went through all my barrier strips and double checked.
