(This also applies to errors logging into any Office365 apps on an Apple computer)
1. Click on the search/magnifying glass at the top right of your screen.
2. Type "keychain" into the search box
3. Press enter on your keyboard to open the "keychain access" window
4. On the left side of the window click on "Login" and then "My Certificates"
5. You should see one or more certificates in the main window that start with "com.apple.idms..."
6. Click on each certificate and press your delete key to remove them
7. Open microsoft word, powerpoint, or excel and try to log in again.
8. You should now get the OBU login page to show up and will be able to log into your office apps.