My Airport Express (2nd generation) freezes up with a solid amber light after updating settings via Airport Utility. All of my devices lose internet connectivity and I have to unplug and re-plugin the Airport Express to get a green light. Once it turns back on, none of my settings are saved.
I finally discovered that this only happens when my D-Link DCM-301 modem is plugged in to the Airport Express. Unplugging the modem and then tweaking the Airport Express settings via Airport Utility works as expected. Weird.