Getting "There are no speakers connected to the AirPlay device ""

For the past several years, I have had a stereo receiver hooked up to and airport express to stream music wirelessly from my iMac to stereo speakers. All of a sudden, I started getting the message "There are no speakers connected to the AirPlay device "<device-name>". So, what changed, we recently changed ISP from Verizon DSL to RCN cable, I changed my Apple ID (due to the ISP change), I upgraded all computers to OS X Lion, and I have a new iPhone5. I can't tell you exactly when during the process things went bad, but I can tell you what I have done to solve the problem:

1. I checked that my devices are configured correctly. The network layout is as follows: I have an Airport Express on the 3rd floor of my house, along with the iMac containing the iTunes library, I have an Airport Express on the 2nd floor acting as a repeater, I have an Airport Express on the 1st floor acting as a repeater and connected to my stereo receiver and 4 speakers. I control which set of speakers is "on" via the receiver.
2. I checked that I can get sound out of the speakers via the receiver by selecting FM and got radio to play, so I believe the receiver is ok.
3. I swapped this receiver with another receiver and got no sound and still the message "there are no speakers connected..."
4. I moved the Airport Express from the AUX port to the TAPE2 port to check the port. Still no sound.
5. I checked the cable with a Bose box and got sound, so I believe the cable is ok.
6. I plugged a headset directly into the Airport Express and got no sound.
7. I swapped the 2nd floor and 1st floor Airport Express units, reconfigured the new 1st floor unit to turn on Air Play and still get no sound and the error message.
8. I am controlling the music using the Remote app on my iPhone. I have configured the new device to use this library.

I am tired, confused and at a loss. What can be going on here?