Applies to all O365 apps. Outlook, Excel, Word
Occasionally your MS account in your O365 apps may not sync correctly with Microsoft. In this case you may see a message similar to this
or you'll notice you only have basic functionality, like read-only.
Most times, refreshing your MS account in the O365 app will fix things. Here's how...
In any O365 app, go to file->account (or file->office account).
Under user information, sign out of ALL accounts.
Sign back in with your email address and email password.
Restart the MS O365 apps.
You should have full functionality back and/or the message should no longer appear.