Windows 7 VPN Cpnnection errors

I've set up the VPN service on my server. I've been thru the setup serveral times and it appears to be correct. When I attemt to log in from a windows 7 Ultrimate x64 machine, I get to the server and then rejected with an error 691. A couple hours of research on line, and I find it's a common problem with multible possible causes, but no one seems to have a sound answer.

The error apparently can be cause from the host end or the client side, but is most commonly found on the client side when running Windows 7 OS.

Please help.