My trusty old Airport Express got a bit damaged recently, and while it still works I figured it was time to upgrade to one of those fancy new Airport Extreme (n) gadgets. So when it arrived I set about replacing the Express with the Extreme. I switched the Ethernet cable from the Express to the Extreme, made a new wireless network with the Extreme as the base station, and configured it exactly the same way as the Express - connect to internet using Ethernet and configure IPv4 using DHCP. As far as I can see all the other settings are identical to the way the Express was configured. Yet the Extreme refuses to work - it consistently claims that ""your base station does not have a valid IP address", despite the IP address it displays in the Airport Utility being exactly the same as the one displayed by the Express. When I switch back to the Express everything works perfectly. I cannot for the life of me see where I'm going wrong. Any ideas? Setup is 2GHz Intel iMac with D-Link DSL-300T ADSL Modem. Much obliged!