DVR recordings of HD channels are now blank

This is a new problem, in the last few months. I assumed at first that a summer storm may have interrupted the channel , so there was only a blank screen to record, but now it is happening more frequently. Almost every time.I changed a few of my favorite shows after missing them due to the recording issue to non HD channels, and they record fine, but this is not fine with my husband who really loves his HDTV. Any thoughts?

And thank you!

(Did reset the receiver already..didn't work and some of the HD channels are not working at this moment as well)