Configuring preferences and options in Outlook.com
Hello Peter,
I'm Diane, an Office Apps & Services MVP specializing in Outlook, and I’m happy to help you today.
Are you using Outlook software installed on your desktop or opening Outlook on the web in a browser? (This forum is for Outlook on the web.)
You shouldn't have calendars in the Favorites section in Mail module.
If it's in Outlook desktop software, the navigation pane is corrupt - you can restart Outlook using the /resetnavpane switch.
Close Outlook. Right-click on the Start button and choose Run or press Windows key + R to open the Run command. Type or paste the following into the Open field and press Enter or click OK to restart Outlook. (There is a space before /.)
outlook.exe /resetnavpane
Note: This will wipe out all folders on Favorites in Mail module and reset the Calendar and Contacts modules to the default format.