I looked to see if tuner sharing was on and it wasn't. I turned it on and still got the same error. I went back to the tuner sharing option and it was greyed out with no ability to turn it back on. I'm not exactly sure what happened there, but I can't tune any channels in that I've tried so far.
At the moment, the HDHR is connected via Ethernet and the Nvidia Shield hosting the Channels DVR Server is on WiFi. That setup was working briefly. I've had issues getting the Shield to function when connected to Ethernet.