- Are you using the correct VPN server name? The server administrator provides this name.
- Is the Internet / network connection to the server functioning properly? You should ping the server is not sure.
- Is your network firewall blocking VPN connections? Port 1723 must be opened and Protocol 47 must be enabled in the firewall configuration settings
- Does the server have too many clients already connected (VPN server connection limit exceeded)? The server administrator can check this, but it is not a common problem.
→ See also - VPN Connection Error 800 (support.microsoft.com)