The problem is that Windows Defender is 'interfering with' Symantec
-- that is, it keeps on trying to open Symantec files --
even though I have cited each of them (there are four folders)
under Windows Defender's
AdvancedOptions>DoNotScanTheseFilesOrLocations.
That makes this Windows Defender's bug, rather than a
[possible] problem with Symantec or Norton. I agree that
Symantec/Norton should have an 'ignore' list, but,
by offering the option above, Micro$oft claims to HAVE the
corresponding list.