I'm building a new machine and everything is working correctly, except that I can't log on to my VPN. It hangs at the "Verifying username and password..." step, then returns after about 30 seconds claiming Error 721.

I have another machine sitting next to this one with the VPN connection configured exactly the same, connecting just fine over the same wifi network, so I'm convinced that there is no server or firewall problem. The VPN works fine. This machine simply can't connect to it given the correct credentials and configuration.

Any suggestions?