Solved, see below:
In Outlook 2007, choose Tools | Trust Center and choose Add-ins from the
navigation list on the left.
At the bottom of the Add-ins screen, under Manage, select COM Add-ins and
On the COM Add-ins dialog, click Add and navigate to the C:\Program
Files\Microsoft Office\OFFICE12\ADDINS folder. Select outbak.dll and click
OK. When you return to the COM Add-ins dialog, you should see a new entry,
Outlook Backup Addin, with its check box checked.
Click OK to close the COM Add-ins dialog.