KB0021 - "Installing Office customization" error starting Outlook 2010

You receive an error Installing Office customization when starting up Outlook 2010 as below:

Issue

You receive an error Installing Office customization when starting up Outlook 2010 as below:

Reason

OnePlaceMail cannot find the file “FileToWSSOutlookAddIn.dll.manifest” in the OnePlaceMail install directory. This file should be in the install directory as below:

Solution

Uninstall OnePlaceMail client and reinstall on the machine. Confirm that the above file is now present, then startup Outlook 2010.