Control Arduino Uno with iPad app via Wifi Shield - doesn't connect


I have gone through all the basic steps to set-up the Arduino Uno and Wifi Shield. After all steps had been completed I disconnected the Arduino (with Wifi Shield attached) from the computer and powered it with a 12VDC adapter. The indicator LED next to "Link" lit up and I assumed that I had a network connection.

Next, I DL'ed iArduino and followed the instructions to install the app and software. This appeared to go according to instruction, too. After opening the app and attempting to follow the basic set-up for controlling an LED I get no response (iArduino: iArduino Tutorial).

Has anyone here used this app successfully? I am wondering if it has something with the way my Airport Extreme is set-up? Possibly incorrect IP address or ports? Any help would be greatly appreciated.