In Microsoft Office 365 dedicated, a delegate is granted permissions to a calendar in Microsoft Outlook. When the delegate tries to change or delete a calendar item by using delegate permissions, Outlook crashes. Or, the delegate receives one of the following error messages:
The item could not be deleted, it was either moved or already deleted, or access was denied.
Could not complete the deletion. The items may have been already deleted or moved.
This issue occurs because the Deleted Items folder is not granted permissions when delegates are set in Outlook. This is the default behavior.
This issue occurs when the following conditions are true:
The DelegateWasteBasketStyle registry key on the delegate's computer is set to a value of 4.
The delegate does not have permissions to the Deleted Items folder of the owner's mailbox.
If the DelegateWasteBasketStyle registry key is set to a value of 4, Outlook tries to move the deleted calendar item to the Deleted Items folder of the owner's mailbox. In this case, one of the errors in "Symptoms" section occurs.
To resolve this issue, grant the delegate at least author level permissions to the Deleted Items folder of the owner's mailbox in Outlook.
To determine whether this issue occurs, the delegate can hold down the Shift key and delete the item. In this case, the item should be deleted correctly.
For more information about the DelegateWasteBasketStyle registry key, click the following article number to view the article in the Microsoft Knowledge Base:
202517 Items that are deleted from a shared mailbox go to the wrong folder in Outlook