I have similar problems with the DCT6416 III boxes from my local cable company but it usually happens around 70 or 75% full. I can try to set to record even a 1/2 hour sd program it will say the hd is full. I can go in and delete some shows so that I am down to say 65 or 70% full and it goes right back to saying the hd is full. I usually have to get it down to around 50%, losing some shows I haven't had a chance to watch, to get it to accept a recording again. This is my 4th or 5th receiver and they all have done it so I think it's a software, not hardware issue.
The reason I have gone through so many boxes is because of problems with the box being slow to respond to remote commands. The most annoying one is when fast forwarding through a commercial and it will just keep on going for 5, 10 or even 20 seconds before it will respond to the remote command. After it starts working again you can see the status bar on the bottom of the screen flashing through all of the commands I was pushing while trying to get it to stop ffwding. It will also lag when trying to skip back. Also when trying to direct access a channel with the number keys almost always has to be done at least twice because the box will miss one of the digits for the channel. For instance trying to select channel 601 it will go to 60 or 61 or 01 instead
Am I the only one with these problems? I honestly expected this forum to be full of complaints with this box not responding to remote commands. Some of the boxes I've had have been better than others but they've all done it to some degree. I'm almost to the point of going back to Dish but the price for my cable/internet/phone package is just too appealing at this time.
These are only the most annoying issues I have with the DCT6416 III, there are others as well. I'm of the opinion that this receiver was put into service before it was sufficiently tested although from reading this forum it sounds like it's been out for quite a while already.
EDIT: I guess I didn't search long enough, it looks like I'm not the only person having problems with this box. Sat tv is looking better and better.