I don't typically post, but this one needs to get communicated...no thanks to linksys... I've implemented several 2k3 SBS installations using linksys routers (WRT54GS) as the firewall. In all instances up to this point I've used the same configuration of port mapping; it has worked fine. My last one I ran into an issue getting the VPN to work; Error 721 everytime, and the VPN connection would hang on "verifying username and password". The error in the SBS Event log: A connection between the VPN server and the VPN client X.X.X.X has been established, but the VPN connection cannot be completed. The most common cause for this is that a firewall or router between the VPN server and the VPN client is not configured to allow Generic Routing Encapsulation (GRE) packets (protocol 47). Verify that the firewalls and routers between your VPN server and the Internet allow GRE packets. Make sure the firewalls and routers on the user's network are also configured to allow GRE packets. If the problem persists, have the user contact the Internet service provider (ISP) to determine whether the ISP might be blocking GRE packets I verified the DSL provider is allowing protocol 47, I validated my VPN works on the LAN side, so I call Linksys.... Asking if there is anything wrong with their latest firmware? NOPE...all works fine they say.... Well here's how I solved the problem: Using the same router WRT54GS V2, I rolled back the firmware version by version using their TFTP client. Nothing working until I got to v3.17.4 and VIOLA... VPN works! Conclusion: PPTP passthrough has issues in firmware later than V3.17.4, I've tried every version available on their FTP site and none of them later than 3.17.4 allow PPTP passthrough. Thanks Linksys for all the help and support.... you can close my ticket.