I've been experiencing this error, as well. It just started a couple of weeks ago, with several recordings on the same Wednesday night being the victims: The Americans on FX and Bomb Girls on REELZ. They showed as recorded, but I got a black screen when trying to view them, and the only way out of that screen was to reselect the DVR button and then choose something else to watch. Both timers were for 2 min. extended recording, but I don't remember now if they overlapped, and The Americans is done for the season, so I can't check for conflict.
The latest instance was last Sunday's Mad Men, which I didn't realize until I tried to watch it today. There is another timer that's set for extended recording at the same time, but they don't overlap, and there are enough timers available (even with PT enabled & recording). If Ghpr13's observation about extended timers is the clue, I'm thinking I'll let the timers run as scheduled, check them when completed, and be prepared to record at least one of them at a later time. Thanks, Ghpr13!
In the meantime, if it's still the consensus that the Hopper is on borrowed time, I guess I'll start shopping for another EHD, since the one I have is getting very full, and contact Dish about a replacement. What fun!