There is an older model of Airport express that can do either 2.4 or 5 Ghz but not both at the same time. While you can't have gotten an old one directly from Apple in the last 18 months, you might have found an older one elsewhere. The new one has a two conductor power cord and the old one had one of those fold out plugs attached directly to the router. New one looks like a white version of Apple TV in shape and size. And there always is that possibility of getting a bad one. Assuming it's still under warranty, take it down to an Apple store and have them look at it. If it's defective, they will replace it.