Windows VPN Error 800 indicates your PC cannot connect to the VPN server. Most of the time, this error happens when the client’s VPN can’t communicate with the server due to network problems, wrong server address, or blocked ports. Besides that, the error can be caused by firewall or antivirus conflicts, DNS issues, or an inactive VPN server. Usually, the connection is dropped even before the authentication starts, which shows that it’s a problem with communication and not the credentials. Therefore, verifying your network setup, server information, and checking if you’re connected will go a long way towards fixing this error.