A Microsoft file hosting and synchronization service.
My situation is good and bad and seems to involve permissions. I've done resets, etc., but without positive effect. My situation is: with shared folders from user A, I can sync, but with shared folders from user B, I lost the capacity to sync, apparently after software updates on the user B computer. These updates included moving to Office 365 from Office 365. Perhaps something is going on with TFA. It would be good to have a troubleshooter app.