Vista Media Center Audio Problems

  I just built a new Vista Media Center (Vista ultimate) and I am having audio
problems with recorded TV copied from my other Vista MC Computers.  With the
copied Recorded TV files I get no audio via HDMI .  If I connect via
headphones I can hear the audio perfectly fine.  I am having the same problem
with DVDs (Retail DVDs i.e not ripped).

I can hear sounds the VMC makes as I navigate the VMC GUI (MC start sound,
button press etc.) over HDMI.

Of course there is no audio with Windows Media Player either.  If I play the
Recorded TV files, or a DVD with PowerDVD or Nero Showtime the audio works
fine over HDMI.  

The problem seems to only happen with Media Center and Media Player, all
other application that I use the audio works properly over HDMI.

Thanks

B.D.