well... the problem is when two , or more lan hosts want to access same vpn server with pptp "microsoft vpn protocol" Only one host can connect to VPN simultaneously
Some vpn servers do not allow more than one connection from the same client address. Reason being that the vpn server tracks each connection based on source address ands gets confused if it gets two from the same. Your two lan machines both appear to the vpn server as the same machine (same source IP address). Something to check.
John