Thank you for your response.
Norton Anti-Virus was my first thought, as Norton had had a problem which I experienced too. They resolved that one with their Sep 30 2015 (22.5.4.24) release (https://community.norton.com/en/blogs/product-update-announcements/norton-2254-p roduct-update-available-now). In any case, my current problem started when iTunes 12.3.1.23 was installed. It is not a Norton security product problem.
Uninstalling the Apple Mobile Device USB Driver and reinstalling it brings the iPod up as a generic storage device in Windows, but it is not recognized as an iPod by iTunes.
I updated the driver from C:\Program Files\Common Files\Apple\Mobile Device Support; it installed Apple iPod USB Driver, and prompted me to restart the computer.
After restarting, all was fine with the first sync. On the second sync, iTunes again did not recognize the iPod. In Device Manager, the Apple Mobile Device USB Driver again displays the above error (text copied here):
Windows cannot load the device driver for this hardware because a previous instance of the device driver is still in memory. (Code 38)
The driver could not be loaded because a previous version of the driver is still in memory.