On second thought, I don't think my systems are the problem. I just ran MCE on another of my workstations, a third, one that I've never used for recording or watching TV on, and certainly never messed with any of Windows' settings (it has no SSD), and on it, too, MCE generates "errors during the last update" of the Guide. Repeatedly. So clearly there seems to be a problem in my household with getting Windows Media Center Guide updates. I'm Oh for three so far.
I think I'll try Media Portal. I was able to determine that I first had to install SiliconDurst's HDHomerun software before MP was able to even see it, then, through trial and error, I finally figured out that the Server has to scan the channels with "TuneQAM instead of ATSC" checkmarked, and to look for "QAM Standard Alternative". Otherwise it sees hardly any channels.
Now if only I could figure out how to just tell it to record . . . It doesn't seem obvious. I sure do miss the ease of Windows Media Center.