Hi Vincent, I'm assuming you since figured out a solution to this, the following 2 solutions are the ones I came across, I used the 2nd one. Works for Outlook 2007 which is where I ran into this problem. Can you update if you solved it another way?
Use the Outlook 2007 Trust Center:
Open Outlook
Navigate the menus through: Tools | Trust Center... | Add-ins (on the left)
Ensure "COM Add-ins" is showing next to "Manage:", at the bottom of the dialog
Click [Go...]
Untick "[ ] The offending extension"
Click [Ok]
Restart Outlook and verify that it worked.
Delete "extend.dat", because the add-ins are cached there.
Close Outlook
Go to My Computer (Windows Explorer)
Navigate the menus through: Tools | Folder Options | [View] tab | "Advanced Settings" section | Hidden Files and Folders
Tick (x) Show Hidden Files and Folders, and click [Ok]
In Windows Explorer, navigate to C:\documents and settings\{username}\Local Settings\Application Data\Microsoft\Outlook
Delete "extend.dat"
Close Windows Explorer, and reopen Outlook
