Issues with Airport Express connecting to gateway

I previously was using an AirPort Express as my router (Ethernet from gateway), with another AirPort Express for my AirPlay on stereo. I've found that the Gateway gives me faster and more reliable internet by itself, so I removed the AirPort Express. Now I can't get either AirPort Express to connect to the existing network to use for AirPlay. I get "an unexpected error occurred" on the AirPort utility when I try to set it up, then the gateway thinks the AirPort Express is connected, but the AirPort utility and the AirPlay settings don't think it exists at all. I tried putting it on a static IP, I tried turning on link local only, and that didn't change anything either. Anyone have ideas?