Outlook 2007 - How to Remove an add-in that no longer exists

For Outlook 2002-2003, go to Tools -> Options -> Other -> Advanced Options
Click on Add-In Manager. Uncheck the offending add-in

For Outlook 2007 there is a whole new add-ins manager.

First, Delete the extend.dat under your documents and settings because the add-ins are cached in there. Go to Start>Search>Navigate to Documents and Settings>Search for extend.dat and delte it.

Hint, you must have hidden files turned on. To turn on hidden files, open My Documetns, go to:

Tools>Folder Options>View, click the radio button called "show hidden files" 

Next: 

1.        Open Outlook

2.        Navigate the menus through: Tools | Trust Center... | Add-ins (on the left)

3.        Ensure "COM Add-ins" is showing next to "Manage:", at the bottom of the dialog

4.        Click [Go...]

5.        Untick "[ ] The offending extension"

6.        Click [Ok]

7.        Restart Outlook and verify that it worked.