This shouldn't happen, but the reality is that this problem does sometimes happen. The problem is not caused by your HDMI cable - instead, it results from a failure of the HDCP (high-bandwidth digital content protection) handshaking process that must occur between the HDPVR and the TV before the HDPVR is "permitted" to send a video/audio signal to the TV. Some makes/models of HDPVRs are commonly afflicted with this problem, and sometimes the problem is limited to specific combinations of HDPVR and TV makes and models.
Rather than trying to fight this problem, my suggested solution is use an alternative method of connecting the HDPVR and the TV. Use a 3-cable component video connection and optical digital audio connection between the HDPVR and the TV, instead of an HDMI connection. The video and audio quality of these two connection methods is essentially identical for a connection to an HDPVR, which doesn't output a video signal higher than 1080i.
