And do I really need to worry about it?
There were no such messages re the C-drive.
Avast said re both messages: "Unable to scan: The system cannot read from the specified device."
QuickTime and my computer are working just fine except for 1 minor problem at the moment, namely the Videochat program I'd like to install (and have before successfully installed and run) only says: "The NTVDM CPU has encountered an illegal instruction." when I try to install; it. But Avast found nothing amiss with that program reading viruses or reading it.