COMCAST VIDEO AND AUDIO THROUGH A YAMAHA RECEIVER. PROBLEMS!!

I have a Yamaha RX-V1600 and a comcast HD Box and when I use the HDMI out from the comcast box into the HDMI in of the receiver and then out from the receiver into the back of my HDTV I am having issues. Does anyone know if Comcast does not allow this sort of third party transfer as I know the receiver will allow it. It is working with the use of a component cable and digital audio from the back of the cable box and directly into the back of the TV. An help would be greatly appreciated.