VPN over Hotspot

Folks,

I have a client trying to do VPN over our hotspot network.

He indicated that while doing the VPN attempt from his client, he gets the username and password request but after that it fails.

I am not sure at this point what type of VPN (PPTP or IPsec) it is.
In doing a torch session, I can see the request for the proper dst-address (being the public IP for the VPN server) but the dst-port shows up as port 0.

Any ideas or insight would be appreciated. I did enable PPTP and GRE on the router.

Thanks

PPTP shouldnt be a problem but, ipsec might have some problems. in my experience i have not had much success establishing an ipsec tunnel through any natted or masqueraded network.