If your RGU app is working but there is no email access or the email pane is showing an error, try the following steps.
Users need to give the app permission to access O365 - this will normally be in the notification area.  If it is not appearing and still not working they should "disconnect" those services under their user profile (e.g. on a desktop go to "services"):


Then "disconnect" each one:



They will then be prompted to allow access when they next try to open calendar/mail.

If this still does not work, please provide a screenshot showing the error, and the address bar and send this to [email protected]