Thanks for the response. I installed CCCP on both machines following the directions from the DirectShow Playback guide on the wiki. I experimented with various playback settings on the client machine. I still get the same error.
I have never had any problems playing the TV recordings on the server machine (the one containing the TV tuner stick, Pinnacle Pro HDTV, and serving up the library) - both before and after installing CCCP. I'd also note, though it probably doesn't matter, that I am using the 64-bit version of Windows 7 and I am recording a digital over-the-air broadcast.
I also tried playback on a different client machine - one that also has Windows 7 and a TV tuner stick and therefore all of the same drivers as the server machine. I receive the error message there also. If I use a local library, I can record and playback TV programs on this machine. However, when it is a client of the server library, it can't play the file on the server.
I tried GSpot on the server machine. I assume that the appropriate file ends with .jts.cnk as the extension. It says that the video codec is MPEG2. Its name is MPEG-2. But the status is "Codec(s) are NOT installed." This doesn't make sense to me as playback works fine on this machine.