I’ve seen a rash of reports lately with people having problems with TFS when configured to use a Fully Qualified Domain Name (FQDN). There are certain extranet scenarios when you need to configure TFS this way. The problem has been isolated to a change in Windows 2003 SP1.
The symptom is error messages that look like the following in your event log:
Exception Message: TF30063: You are not authorized to access https://teamsystem.contoso.co.uk:8081/. (type TeamFoundationServerUnauthorizedException)
Read the following KB article to understand the issue and learn how to correct it: http://support.microsoft.com/kb/926642