Remote access

Please can somebody help this is really killing me that it won’t work. I have set up my server (windows 2003 web edition) as a RAS server. I have given accounts in active directory rights to log on remotely, I have disabled firewalls and everything else I think possible to get remote acces VPN to work. However, when I try to connect a client it connects to the server but cannot authenticate the username and or password (error 691). anybody any ideas?