Thanks for the suggestion.

Yes I did reboot with no change. I installed the latest build of BIAB and tried again. This time, not only would Pro Tools not open, but it rejected the BIAB DAW plugin, saying that it is not a valid 64 bit AAX plugin.

This is so frustrating - I am in the middle of a Pro Tools project that I have to finish by year's end and now PT will not open up.

I am using Windows 10.x with build 608 of BIAB 2019, an HP ENVY Pheonix 810 PC which has 8 co-processors and a 2 TB internal disc and a 4 TB external disc and a Yamaha AG06 audio interface, ProTools v 11. I have been using BIAB and ProTools simultaneously for years with no problem.