I will try that. BUT HERE IS THE MOST INSANE THING! I have BIAB fully installed on a peripheral hard drive. I plugged it into my older Mac Mini. I opened a session and was able to save the session (as a BIAB 2017). Then I tried it again, and it failed to save!!!!
I got the same notice. NOW HERE IS WHERE IT GETS EVE STRANGER - - - I disconnected the peripheral hard drive and opened BIAB 2015 which was stored on the hard drive of the Mac Mini. I tried to save a session and it failed with the same warning - "Error: Cannot save to root of drive" - - - - so whatever is wrong migrated into the BIAB on the Mini and now that computer is all screwed up.
I talked to Apple support. "Error: Cannot save to root of drive" is not even a recognized Mac problem - it is not in their manuals! Apple has never heard of it before!