I have the same problem that happens a few times a week with the SA 8000HD DVR.
I usually keep my cable box in 480p mode.
Sometimes just flipping the channels makes it go away.
The full proof way is to change the cable box resolution to 720p or 1080i and it goes away.
Sometimes I do the change with the box tuned to a HD channel.
This should work.
As far as a fix, forget it, I have Comcast and they don't know anything, even their tech support, If it is not in their data base, they don't know what to do, they always want to send someone out to replace the box. Most of them have no idea of what Firmware is.
To find out what firmware you have do the following
On the box (NOT the remote), hold the center OK/Select button down until the message LED starts flashing. Then press the Info button. that puts the diagnostic pages on the screen of your TV. On the remote, press Page Up/Down to flip thru the screens. Press Exit to get back to watching TV. The software versions are on one of the pages. Please check and report back your SARA vers, and whether you have firewre working.
Hope that works for you....