I have an Airport Extreme connected via ethernet to a modem which supplies the internet to the house. I have two airport express stations wirelessly extending that one extreme. The other day one of my airport express base stations came up with the error "cannot extend wireless network. I power cycled the router, set it back up and nothing works. All the settings match the airport extreme. It was working until about 4 days ago. Any ideas on what might be causing the issue?