Starting with the RC0 release of Windows Server 2008, Terminal Services Web Access (TS Web Access) requires the most recent update to the Remote Desktop Connection (RDC) client software. This updated version is available in the beta versions of Windows Vista Service Pack 1 (SP1) and Windows XP Service Pack 3 (SP3).
If you are taking part in a Microsoft Connect Beta program, you can download the beta versions of Windows Vista SP1 or Windows XP SP3 from the program Web page.
If you are not an administrator, and you are using TS Web Access at your workplace, contact your system administrator to determine whether your workplace is participating in a Microsoft Beta program. If it is a participant, your system administrator can help you to obtain the updated RDC client software.