Just one thing I discovered and more than obvious when you think of it. The account you use to restore the Exchange item must have full access to the mailbox.
"Exception of type 'System.Exception' was thrown"
was the result during the restore.
Strange thing was that after I added the Full Access permissions to the mailbox it took more than 5 min before I could actually restore the item. Not sure why it took so long before Veeam could actually restore the item.
Just thought I shared my experience.