I am using Outlook for Mac 14.3.9, I have the outlook.com account set up using imap.  For the last 3-4 weeks I open Outlook for Mac, all accounts connect/sync without a problem.  I usually leave my email open while I am working, and I will intermittently receive the following pop-up message

The server for account "Outlook.com" returned the error "Logon failure: unknown user name or bad password." Your username/password or security settings may be incorrect. Would you like to try re-entering your password?

If i cancel it, the account my sync, or it may pop up again, but it will eventually sync without problem.  This does not occur on Outlook for windows, or on my iPhone which also uses imap to connect.

Any suggestions...