I have the same issue. Originally I had the "An unknown error has occurred, the error code is: 0" error, after which I followed the directions in the link above. Now I get the error "The system requires that you sign on to a valid account" when trying to activate Outlook 15.3 (141024) on OSX 10.10.1 (14B25). I can use the same credentials to login to the web app and to access mail with Mail.app. Help?
↧