I just read this possibly-relevant bit of information: "Outlook Express is no longer supported and has been removed from Windows entirely. Microsoft's free email client is now known as Windows Live Mail, and must be downloaded separately. Outlook Express is not supported and will not work under Windows 7."
It's in this post: http://www.tomshardware.com/forum/7686-63-common-questions-windows-version
, point number 19. I know that you had full Outlook, not Express, but this is as close as I can get.