When you receive an error message in Outlook 2003 that says you have an error in the registry for Exchange Extensions: "The syntax or format of the registry entry is incorrect. Check the registry and compare the registry for this extension to other extensions in the registry." This error means you have a corrupt registry key. While you can edit the registry to fix the problem, you really should upgrade to the latest SP for Outlook 2003 to correct it for good.
See //support2.microsoft.com/kb/823633 for more information.
Published August 1, 2005. Last reviewed on June 17, 2011.