I have followed this link to setup my VPN on Windows 2003 box http://www.wintips.org/how-to-setup-vpn-server-access-in-windows-2003-one-1-nic/
On router I have forward port 1723 to server internal IP address.
From windows 7 client I have setup a VPN connection point to external IP of my router.
The connection fails with error 800.
I have disabled the third party firewall I have on the server but the problem persists.