Cisco 1841 with firewall / Windows 2003 VPN Server

I have recently installed a Cisco 1841 route with the Security Bundle, if I do not enable the firewall the remote VPN connections work fine, but when I enable the fire the connections fail. The Windows VPN server log show the user connection timed out is there a way I can tell the firewall not to inspect the port that the connection is using ?

Thanks
Benny