Thanks for the feedback, Glenn!
I've never had XP10, and started fresh with XP11 in October, so there isn't any conflict there.
After looking through the log file, I traced back most of it to my SPADnext installation. I thought I had disconnected the SPAD XP plugin, but I hadn't, so it was continually trying to connect. I have removed/deleted that.
Based on the timing of when this error began, it seems it might be an Actice Sky XP issue, rather than an X plane issue.
Thanks for your help troubleshooting, though. Much appreciated!