Google is your friend. MS says (at
http://support.microsoft.com/?kbid=827349) that Outlook is broken and cannot be repaired. You should give up and use some other mail client, if that's an option for you. In my case, the Navy dictates that Microsoft is god, king, judge, jury, and executioner, so I'm SOL, but there may yet be hope for you. (sigh)
Seriously, the MS support site basically says you need some upgrade patching stuff. Looks like your outgoing mail server probably changed what they were doing without telling you, and your machine, being infested with Microsoft crud couldn't adapt.
Dan