Problem

If you are having trouble deleting appointments on a shared calendar (including resource calendars) in Outlook for Windows and you see the error message below. 

Solution

Method 1: Exit and restart

Exit all clients (such as Outlook and Outlook Web Access) on which the mailbox is set up, start Outlook, and then try to remove the item. 

Method 2: Use Outlook on the web

Log into Outlook Web Access (OWA – https://mail.utoronto.ca) to delete the appointment.

Additional information

Additional methods from Microsoft