Using MS Mail w/Outlook 2003

[CEV]

I know, I know, MS Mail is no longer supported. But I am at a loss here and
I'm hoping someone can give me some insight. I have about 4o users using MS
Mail with either Outlook 2000, Outlook XP, or Outlook 2003. I have been
setting up some new pc's for users and configuring them with Outlook 2003.
There is 1 pc that is not working.

Here is a list of what I can do:
1. I can send Internet email.
2. I can reply to an email that was sent to me when the user used MS Mail.

I cannot send a new message using MS Mail. I can select a MS Mail recipient,
but when I hit send I get an error that states "The operation failed. An
object could not be found." You can only select OK and it does not send.

What I have tried:
1. Restarted PC.
2. Restarted the PC that MS Mail resides on.
3. Removed and reconfigured MS Mail in Outlook on the users PC.
4. Did a repair install of MS Office 2003.

Everyone else works with MS Mail except this one pc. I am at a loss as to
what to try. We will be switching to Exchange Server this fall, but I need
MS Mail to work until then.

Please provide some input.

Thank You,

Chad