I have set up a router with DD-WRT Mega on my Asus WL-500gP V2, and I can't connect to the VPN service. I have set it up according to the configuration on the DD-WRT wiki, so the server IP is set to 192.168.1.1, which is the address of the router, and I set up the client addresses to be 192.168.1.20-29. My chap secrets are set up correctly, and still, I get an error 800 on windows XP.
As far as I can tell, it means my network is unreachable.
The server responds to ping.
[Edit] If I manually edit the connection so that instead of "Automatic" I set it manually to "PPTP", it fails. I disabled the enforcing of security, and it still fails.