Make sure computer and airport express are on the same network
Make sure speakers are turned up loud enough
Make sure nothing is interfering with Wi-fi signal
Make sure switch under button is turned on
Try turning on the transceiver's address code to make sure signal is getting to transceiver
Try plugging transceiver into another outlet
Make sure the command is in the speakable items folder
Try changing the name to something easier to pronounce clearly
Make sure script was saved as an application