A connection between the VPN server and the VPN client %1 has been established, but the VPN connection cannot be completed. ...

A connection between the VPN server and the VPN client %1 has been established, but the VPN connection cannot be completed. The most common cause for this is that a firewall or router between the VPN server and the VPN client is not configured to allow Generic Routing Encapsulation (GRE) packets (protocol 47).