Outlook 2003 cannot access Exchange 2003 server

[toksoladuti]

A user had Office 2000 installed which worked fine with our Exchange Server 2003. He upgraded to Outlook 2003 but then could not access Exchange 2003. He gets the following message: "Your Microsoft Exchange Server is Unavailable" It then gives you the option to: Retry, Work Offline or Cancel. I get a similar message if I try to re-create the profile. I have checked the RPC entries in the registry but this appears to be all there. I've also reinstalled Office 2003 but still can't access Exchange 2003. All others and workstations can access the Exchange without any problems. Any help would be greatly appreciated.

Thanks.