PPTP VPN Error 721

Hi Everyone Recently I have been noticing a problem with certain users joining our VPN via PPTP with XP SP2. The Client gets to verifying username then disconnects with error 721. On the RRAS server there is an error of 20209 when the client try’s to access the server. I know there is no problem with the network topology as other users can join without any issues and the error still happens when the user try’s a pptp connection to our Cisco Pix. In regard to the client I have tried "netsh int reset all", deleting and reinstalling the pptp miniport , resetting Winsock by netsh and deleting the key, reloaded the tcip stack from the inf file ,removing automatic updates, reinstalling sp2 yet the fault still occurs. I also read that the issue might be connected to ICS and NAT transversal but that does not fall in to the demographic of the varied clients, to be frank I am stumped and I was wondering if anyone had any ideas before I have to call the remote users back to reinstall their laptops.