"The L2TP-VPN server did not respond"

I just bought an Airport extreme base station, and installed lion server, and configured it for VPN. I have checked all my settings and even looked using AirPort utility. I have tried connecting to my VPN from 2 different Macs and an iPad, and all yield the same error:"The L2TP-VPN server did not respond". When I look at my vpnd.log it is pretty bare:

2011-08-31 18:27:34 EDT Loading plugin /System/Library/Extensions/L2TP.ppp

2011-08-31 18:27:38 EDT Listening for connections...

it looks like the VPN connection requests aren't making it from the airport to the server. Any ideas