Microsoft Outlook + OnePlaceMail
You have previously installed OnePlaceMail in Outlook 2007 and you perform an in-place upgrade to Outlook 2010. You uninstall OnePlaceMail and install the Outlook 2010 version of OnePlaceMail, however, OnePlaceMail Outlook addin fails to load after the upgrade.
After adding the VSTO_SUPPRESSDISPLAYALERTS environment variable and setting it to '0' following the instructions in this kb article you receive an error message similar to the below when starting Outlook:
The reason is that the OnePlaceMail Outlook Addin is trying to load using the incorrect version of the .Net Framework. Outlook 2010 has prerequisite .Net Framework of .Net 4 which is greater than Outlook 2007. As Outlook 2007 was installed previously there is a registry entry telling the VSTO framework to load the OnePlaceMail using the wrong version of the .Net Framework. The solution is to:
Delete the key that corresponds to the Guid of the OnePlaceMailOutlook Addin and restart Outlook 2010.
3. Restart Outlook (the delete key will be recreated)