I'm receiving an error message while trying to run my VPN

Error 766: A certification could not be found. Connections that use the L2TP protocol over IPSec reuire the installation of a machine certificate, also know as a computer certificate.

I have windows vista. I setup my VPN according to your site but my setup options differ from your step by step setup options. I have no way to connect and I have no idea how to make Lineage 2 run with this VPN program. Can I please get some help, thank you.