Error 721 through Cisco FW, no error through dial-up.

[solomongrundy]

I'm as trying to connect to a remote W2K VPN server I've setup at a remote office. When I try to connect to this W2K VPN server with my W2K Pro client I get stuck at "Verifying User Name and Password" and it eventually errors out with error 721. This connection is going through a Cisco 1605-R with IP/FW. If I take the same W2K Pro client, connect via a dial-up going through the same ISP my Cisco is hooked up to, I can successfully connect to the remote W2K VPN server. I've also connected to W2K VPN server from other sites. I think something in the Cisco configuration is blocking traffic at some point. I can telnet to port 1723 on the remote W2K VPN server from W2K Pro client while behind Cisco. Am I missing some other command in the Cisco config?