559 votesDP commented
DisableAADWAM worked for me. Mine is Windows 10, 64 bit. I use Outlook 365.
I followed this process as shared by DustinP....
A step by step for those (like me) that were a bit rusty:
navigate to the file path on the left side of screen to HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity
once at the above location, rigth click in white space on right hand side (or on the top tabs Edit>New), select DWORD (32 bit). Note- My laptop is 64 bit but I still chose 32 bit option and it worked.
give it the exact name "DisableAADWAM"
double click (or right click>Modify) on DisableAADWAM and change its value to 1