You cannot start a remote application or connect to a remote computer on Forefront Unified Access Gateway
On a computer that is running Windows Vista or Windows Server 2008, you cannot start a remote application or connect to a remote computer that is hosted on Microsoft Forefront Unified Access Gateway.
For example, you try to start a remote application by creating a browser session to connect to a Unified Access Gateway Web portal. In this case, the connection fails and you receive the following error message:
Your computer cannot connect to the remote computer because the RDG server is temporarily unavailable.
For more information on this issue, including potential causes, workarounds, and resolutions, see: Microsoft KB Article KB979544.