I'll Eleventh That
Since there have been firsts, seconds, thirds, and beyonds, we'll call this an "eleventh." I can't pin down exactly when it started, but the majority of my USB devices are now unusable in Parallels. Each time I try I get the message about the device being in use by one of my Macintosh applications... Even when Parallels is the only thing running on my system!
I did check the programs that launch at startup, and none of them should be using, say, my printer/scanner combo (EPSON).
I really need to access several USB devices under Windows so, for now, Parallels has become useless. Consider this another plea for a fix!