Outlook has changed their approach to calendar sharing permissions. However, you can now work around the error and manually upgrade the calendar sharing to use the new approach.
To manually upgrade a shared calendar to use the new approach both the calendar owner and the user who needs to schedule to the calendar should log in to Outlook on the web and follow these steps:
1. The recipients have to remove the calendar that was previously shared to them.
2. The calendar owner has to re-share the calendar in Outlook on the web.
3. The recipients have to re-accept the shared calendar using Outlook on the web.
Now the recipients who accepts the invitation should be able to view the re-shared calendar on Recruiterflow.