Terrible problem. Cannot save a BIAB session - a feature in BIAB2017 might have crashed everything (on a late model 2015 MacBook Pro).

I cannot save a BIAB session. When I try I get the message ""Error: Cannot save to root of drive" - - -NOW HERE IS THE CRAZY THING - I have my BIAB program on a peripheral drive and on a backup drive. I get the same message no matter which drive I use even though I disconnect each drive when I boot up the other. I do not have the BIAB 2017 program installed on my MacBook hard drive. IT WAS WORKING FINE until I tried a feature of BIAB - that was to save/render a video of my session to YouTube. The computer said it rendered but it did not save to my hard drive. It was after this that the problem started.
So let me re-state something - I have BIAB full install on one drive - it worked. But now when I try to save a session I get the error message. I then disconnect that drive from the Mac and plug the other one in - I get the same message. I CAN SAVE FILES OF EVERY OTHER PROGAM MY MAC RUNS - THIS IS BIAB SPECIFIC. What could possibly be the problem? HERE IS ANOTHER CRAZY THING - I Google the problem and there are not even any Error: Cannot save to root of drive" problems for the Mac mentioned - only for PC's. I am going crazy here - BIAB no longer usable for me.