Well, I'm not exactly sure what we did, but it is working now. Unfortunately, I don't know exactly what fixed it, but here's a few things to check:
Download the latest firmware to the RC, which can be found here:
http://www.ifirobotics.com/docs/frc-master-ver15.zip
Try tethering to the OI at least once first.
The OI needs to be on and communicating properly for the RC to output to anything.
Make sure you have your backup battery plugged in.