Got a Cisco 881W that you enabled the firewall on and broke your PPTP Tunnel and turning it back off don’t work? That crap happened to me.. You have to allow GRE (Port 47) to pass. This is what I found…
All basic traffic like HTTP, HTTPS, Live Messenger … passes through the router but a MS-VPN client installed on PCs on the LAN is unable to connect to the remote VPN-server.
First a PPTP connection is made, but after that, the logon screen never appears and a
timeout popup shows up. When I remove all lines in the CPP Edit Firewall Policy (similar to disable firewall) the logon screen apears and a connection can be made.
If it is a PPTP connection in addition to TCP port 1723 which you have already allowed you need to allow GRE through your firewall. Note that GRE is not TCP/UDP or ICMP. It is it’s own protocol number at the IP layer.
access-list 101 permit gre any any (assuming that your existing acl is access-list 101)