Can you provide details of the rules you have created to allow these PPTP connections to pass through your Firewall?
Thanks for your reply. The rules are below.
2.) A rule to allow from virual burb to the internal network
You will benefit from looking at my answer to your other VPN post.
As you have now hopefully established there is no on-box PPTP functionality on the Firewall and ISAKMP is not part of the PPTP service - not that I am aware of anyway.
You need to have a PPTP server installed on your internal network and then create an ACL allowing TCP port 1723 (for the initial connection) and IP protocol 47 (for the tunnel) which redirects through the Firewall to that server.
While many of the customers I work with now use SSL-based solutions for their client VPN access, I still have a number quite happily using PPTP using the method I have described.