One channel that I record freezes at about the 40 minute mark. If I play or fast forward from the freezing mark the image stays the same on the screen. I've had a tech in who checked the back end and I'm told everything is as it should be. I tried adding 30 minutes to the end of the recording time and that, not surprisingly, did not help.
It sounds like the start of a hardware issue. One of two issues are common enough to figure out. Does the box get very warm when recording? Heat can cause a number of components to fail, freeze, or stutter due to exceeding the thermal limits of the hardware. Hard drive failure is a little more complicated depending on how the drive is starting to fail. The occasional write fail can be from a number of different reasons but it also might be fixable. Have you tried formatting the drive through the PVR's settings? If the issue persists after you have formatted the drive, it is more than likely that the drive is slowly failing. It will only get worse the more you use it until the drive fails.