Want to get rid of unwanted, useless popup

All of the Outlook 365's in my organization have started displaying this prompt at the start of a session:

All you can do is hit cancel.  Everything works and you are connected to the Exchange Server, but it keeps repeating at the start every time.  Outlook displays a "password needed" message at the bottom of the frame, but if you click it, it just displays the useless prompt again.  If you click Outlook in the taskbar while the message is displayed, it identifies the popup window as "Microsoft Outlook Credentials." The credentials HAVE to have been accepted, or Outlook would be unusable.  Isn't there any way I can get rid of this nuisance?