WIN XP SP3 machines unable to connect with RDP from SBS 2011 web site

If you are unable to connect to an Office computer using the web site (remote.domain name) and you are running Windows XP SP3, click on the link below to apply a fix from Microsoft.

http://support.microsoft.com/kb/951608

The problem is that WinXP does not have Credential Security Support Provider (CredSSP) install and enabled by default. This is a required security feature of Windows 2008 server and must be running.