When you ran the test did you stop the Routing and Remote Access service?
1.On the VPN server computer:
If needed, stop the Routing and Remote Access service using the Routing and Remote Access or Services snap-ins. This step ensures that Pptpsrv.exe can use TCP port 1723 and IP protocol 47.
Generally you should not need to configure GRE Protocol 47 manually in the firewall.
Do you have any other anti-virus or anti-trojan software running on the server that may be blocking the incoming PPTP VPN traffic?
Is this a one NIC server behind a router or a two NIC server connected directly to the public internet?
When you run the test or try the actual connection is this from a remote site on the public internet or over your local LAN?--
"When all else fails, read the instructions..."
MS-MVP Windows Desktop Experience