quoted from
http://www.ms-mvps.com
Error 800: Unable to establish the VPN connection. The VPN server may be
un-reachable, or security parameters may not be configured properly for this
connection.
Resolutions:
1) if you have firewall, open TCP Port 1723, IP Protocol 47 (GRE).
2) make sure you can reach the VPN server by using ping. Sometimes, poor
connection can cause this issue too.
3) You may need to updated firmware on a router or firewall if other OS
(win9x/nt/me/w2k) works except XP.
4) The VPN server may not be able to get IP from DHCP for the VPN client.
So, you may want to re-configure VPN host networking settings. For XP pro
VPN host, go to the Properties of the VPN>Network, check Specify TCP/IP
address and Allow calling computer to specify its own IP address, and
uncheck Assign TCP/IP addresses automatically using DHCP.
5) Make sure other secure software blocks your access, for example, if you
use Norton secure software, you may need to add the remote client's IP so
that the client can access.
--
For more and other information, go to
http://www.ms-mvps.com
Don't send e-mail or reply to me except you need consulting services.
Posting on MS newsgroup will benefit all readers and you may get more help.
Robert Lin, MS-MVP, MCSE & CNE
Networking, Internet, Routing, VPN, Anti-Virus, Tips & Troubleshooting on
http://www.ms-mvps.com
This posting is provided "AS IS" with no warranties.