Ahhh, my X10-World is now back in sync. Good thoughts from both Boiler and JeffVolp. Thanks also to Brian H and *Car*. I gave everyone big helpful.
Anyway, here's what I learned in my testing. It came down to an extension to a circuit I installed a couple of weeks ago in the garage. I added a couple of PSC01 Poweflash units to turn on a warning light inside the house to indicate the garage doors were open after dark. Which, by the way, works very well. But apparently causes noise in the troublesome circuit. By putting an XPPF noise filter on each of the PSC01s ... the problem goes away.
So the reason the downstairs outlets worked and the upstairs outlets didn't work is, as JeffVolp said, probably because of the wiring distance. Thus the noise had more affect on the upstairs outlets. Interesting too, is the breaker for the garage circuit is at the top of the electrical panel. And the other circuit was at the bottom of the electrical panel. Oh well, I'm still learning. And yes, JeffVolp, my X10 is getting pretty large. But it's always been pretty stable, because I've incorporated a lot of stuff that I've learned right here on the Forum.
Thanks everyone for your help.