I had an installation of Kaspersky AV Trial. And after I removed it, my Outlook 2007 started to give an error that it cannot find the addin and it will be disabled. This happens every time I start Outlook 2007.

It appears, Outlook caches the addin info to a file called extend.dat. To get rid of the error, simply follow these steps:

1. Close Outlook 2007.
2. If you haven’t done it before, open "My Computer" and then from that window,
Tools>Properties>View>Hidden Files and Folders and then tick the "Show hidden files and folders" option.

This will enable you to see the hidden files/folders.

3. Browse to C:>Documents and Settings>User Name>Local Settings>Application Data>Microsoft>Outlook and then delete extend.dat.

Start Outlook 2007 and error should be gone