This sounds disturbingly familiar. Just got a fairly upset call from my wife that she was trying to watch some of the Olympics recordings from last evening and was greeted with the "Error code 04" message.
All of our A/V equipment is on UPS', so the "power failure" excuse does not fly, and there was no significant weather events last night so I'm not buying the "signal loss" excuse either. Additionally, when we have experienced signal loss issues due to weather, etc... The unit has reported that during playback with a message similar to "partial loss of event due to signal loss", but has not just refused to play back the program at all.
Next random guess???