My Airport Express was blinking amber and I could not get it to rejoin my LAN. Here's what I discovered and it works like a charm. You need to make sure that you select WPA2 for both devices and encryption type "WPA2 Only". Then, if your "express" is showing up on the WDS page of the Airport Admin Utility - DELETE IT and then search for it again with the "+" sign. Then just follow the next window's instructions and remember to change the password from "public". Good luck!