Outlook – Policy does not allow granting permissions at this level
This issue occurs when an internal recipient is also in your Contacts list in Outlook. When you add this recipient to a Calendar Sharing message, the autocomplete feature of Outlook adds the recipient to the recipient list by using the recipient’s external email address.
To work around this issue, select internal recipients directly from the global address list. To do this, follow these steps:
1. In the Sharing invitation, click the To button. The Select names window opens.
2. In the Address, select Global Address List.
3. In the Search box, type the recipient’s name.
4. Select the recipient to whom you want to send the invitation, and then click To.
5. Repeat steps 3 and 4 for each internal Exchange recipient to whom you want to send the invitation.
6. Click OK, and then click Send.