The cleanups did not work as I got the same message again, but using my wife's laptop to download ZA & then installing it from a USB drive to my computer finally did! So, although no longer frustrated, I'm totally mystified as to what it was that my computer didn't like. You certainly helped put it through all its paces.
Your time and effort on my problem are much appreciated. I just hope there isn't an upgrade to ZA any time soon.