Is your OSX firewall active? If yes, is it configured to allow LW full access? See instructions at the top of this thread Connection problems? Check here first! (click on link)

Also, I'm not sure about airport. I do know some devices you need to reboot in order to properly save the settings (as in my router.) Check your settings were properly saved in airport manager. Also consider temporarily disconnecting the airport. I'm not sure how it operates so ... Also consider rebooting computer.

Also, are there any other connection devices besides the airport?