Look at this thread for possible help...
http://tinyurl.com/b5jhe

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Al Jarvi (MS-MVP Windows Networking)
Please post *ALL* questions and replies to the news group for the mutual
benefit of all of us...
> I have multiple PC's behind a firewall with port redirection set up to allow
> remote desktop connections. I cannot use the default 3389 port because if I
[quoted text clipped - 4 lines]
> to connect it works using the non-3389 ports but the web based
> (http://IP_ADDRESS:port_number/tsweb) will not