On a Windows XP with Office 2007 I kept getting the error “not implemented” whenever I tried to “reply”, “reply to all” or “forward” an email. I also got the error when I clicked on “send/receive”.
Using office diagnostic from the “Help” menu did not help.
Trying to repair the Office installation from “Add or remove programs” or from the CD did also nothing. The error was still there.
What I did was instead of choosing “repair” I choose “Add or remove features”. Here I just expanded the Outlook features and did nothing more that clicking next. Then the setup ran for a little while and completed successfully. After that the Outlook worked perfectly again 
Actually the setup shouldn’t be doing anything because no options was changed, but it seems like it dos fix something that the “repair” function doesn’t.