This article will instruct you how to disable shared calendar improvements. This is very often a fix for not being able to view or edit shared calendars that you are supposed to have access to.
Open Outlook.
Click "File"
Click Account settings, then Account settings again as shown:
Click on your email address, then click change:
A window will open, click on More settings:
Another window will open, Click "advanced" Then ensure that the highlighted box "turn on shared calendar improvements" is UNCHECKED:
Restart outlook and verify if the issue has been corrected.