Recently I have been configuring a Linksys WAG200G router to allow VPN access inbound.  Everytime it attempted to make a connection it would return Error 721.  After a chat with Linksys Tech Support they sent me through some updated firmware that is not available on their website.  So if you encounter inbound VPN issues with a Linksys router contact them and request updated firmware, the version I now have is 1.01.05(1), and it works!