If you receive an error message when Outlook loads that states an add-in cannot be found, it’s because the profile is looking for an add-in you don’t have installed.

The error you receive may be one of these or something similar:

• "<path\filename> is not a valid Office add-in"
• "The add-in could not be installed or loaded"

To correct this you need to verify the add-in is not listed in Tools, Options, Other, Advanced Options, COM Add-ins or Add-in Manager then delete the extend.dat file.

Extend.dat is a hidden file at C:\Documents and Settings\username\Local Settings\Application Data\Microsoft\Outlook. Use the Advanced search option to search hidden files and folder.

If this doesn't help, you may need to edit the registry to keep the add-in from attempting to load. Browse the registry to
HKEY_CURRENT_USER\Software\Microsoft\Office\Outlook\Addins\<addin-name>
HKEY_LOCAL_MACHINE\Software\Microsoft\Office\Outlook\Addins\<addin-name>

If you know absolutely which add-in Outlook is attempting to install, delete the entire key for that add-in, otherwise, change the load behavior to 0 for the suspected add-in.

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Last reviewed on Sep 12, 2011