SOLVED!
After a great conversation with Brett at URC, it was determined that this particular STB is extremely sensitive to IR emitter placement. I have never seen a cable box that was so fussy. Brett has. I was at the customer's home this morning and had to move the emitter about 1/4" at a time...4-5 times...before finding the sweet spot. Now I can run 80 = 100 favorite channel macros without any misfires. If it happens again, I told the customer it's time for a new STB. Brett had numerous other ides to try, but this was the last thing on the list to try. Thanks to all who posted great ideas in an effort to solve the problem.
THANKS TO BRETT K AT URC FOR THE GREAT SUPPORT!