VPN access with cisco Sb-101

Hello,
I am have a Cisco Sb-101 router\firewall at one of my locations. I am looking to setup VPN access through PPTP. I have ran the RAS setup on the server and configured for remote access, when the firewall on the cisco is enabled I can not connect, when it is disabled I can connect no problems. I have opened ports 1723 on the router. Firewall on the server is disabled. In the server event log it is telling me the problem may be with GPE and protocol 47. Your help is appreciated.