It would seem that I would benefit most regarding solutions specific to the error I reported - not general maintenance procedures.
Incidentally, I've already run chkdsk on both drives - no errors. I've also run SFC - no errors. No other info in the event log regarding this error.
Note: I only get this error when I manually configure the backup to include internal drive D, but I can find on APPX file on drive D - hidden or not.