I have 3 HD STBs and 1 HD DVR. I have been enjoying the multiroom viewing of recorded shows for over a year. Now, when I attempt to watch a DVR'd show on any of the STB's, after I hit the final "OK", all I get is the info bar at the bottom of the TV screen with the DVR'd program channel and name, it does not start playing, then after a few seconds, the screen goes completely black, eventually reverting to the last menu of the DVR controls where I selected the recorded program. It's acting like there is a blank recording being sent from the DVR to the STB after the last "OK" is pressed, and the screen reverts to the last command prompt. If I try watching a recording from the DVR itself, all is normal, recorded programs can be watched, so the DVR is capable of playback, just not able to send a playback thru one of the STB's.
Have you attempted to reboot all of your STBs and router?
You can also go to:
From the DVR it will show you the connection status
From the HD DVRs it will show you the connection status plus connectivity to the DVR.
Make sure its all working but at a minimum reboot the VZ router and all your STBs.