Error Description:  806: The VPN connection between your computer and the VPN server could not be completed. The most common cause for this failure is that at least one Internet device (for example, a firewall or a router) between your computer and the VPN server is not configured to allow Generic Routing Encapsulation (GRE) protocol packets. If the problem persists, contact your network administrator or Internet Service Provider.

 

Possible Cause: PPTP uses GRE (Generic Route Encapsulation) protocol to encapsulate the VPN payload in a secure manner. This error generally occurs when some firewall on the path between client and server blocks GRE Protocol (i.e. IP protocol number 47).

 

Possible Solution: Allow both outgoing and incoming Protocol 47 (GRE) on any in between firewalls. If that is not possible, deploy OPENVPN based VPN tunnel on the VPN client – that allows VPN connection across firewalls, web proxies and NAT.