Issue connecting 2 computers on the same LAN to a VPN using PPTP.

I am assisting a friend with an issue that recently came up. He and his daughter use a PPTP VPN connection to connect to a remote file server. They have always been able to connect moth computers to the VPN at the same time. Enter Comcast. Comcast replaced their hardware with a TG1682G. Since the switch they can only connect one computer at a time, the second connection will just time out. I've have looked around for an answer and am having a hard time matching to this issue. Is it a limitation of the router? Is it a configuration issue? IP schema? Also, they are using the Windows Built-in VPN client. Any help would be greatly appreciated. If this question is more suited for another sub, please let me know.