Thanks, Jim, for the suggestions.

The version of CHIRP I've been using is "chirp-daily-20140601-installer.exe".

This is on a Dell XPS L502X with Windows 7 Home Premium edition (with Service Pack 1), 64-bit.  My USB ports are USB 3.0, but I've never had a problem with their being 3.0 instead of 2.0, except for a puzzling USB 3.0 flash drive I once tried, but as far as I know that problem could have been "anything"; I did not have time then to try to diagnose the problem; so I returned the flash drive back to the store for a refund.

In response to your suggestion, I tried the UV-B5's RESET as described in the manual, namely, turning on the radio while pressing and holding the [FM] button.  But the radio did not seem to do any resetting.  I surmise from the manual that I was supposed to get an option displayed of "VFO" (for frequency reset) and "ALL" (for resetting everything resettable).  But I got nothing like that.  And my channels were all still programmed as I had programmed them.  (But before I did any of this I transferred the channel-programming data back to the UV-B5 from the OEM channel-programming software just to be sure I could do that without any problem.)

But in case there was some sort of subtle reset when I tried the RESET procedure, which conceivably might have resolved the original problem, I afterwards tried reading the UV-B5's channel info via CHIRP.  But I still got the usual error message and no apparent transfer of data.