So I have a user that is a delegate for an attorney. When she tries to update an existing entry or create a new entry it wants to send an invitation to the mailbox owner and shows the invitation from the delegate ( please see attached screenshot). I've confirmed the delegate has editor permissions to the mailbox. To get around this I remove the shared calendar and add it back. That'll fix it temporarily. It's happened to a handful of users. We are running Outlook 2010 and mailboxes are on Exchange online. Has anyone else had this issue?