Error Message when Playing DVD Files in Media Center

All:

In the last week or two (no major changes made to the system), I have been
getting the following error message when I attempt to play a ripped DVD TS
folder or ISO image in Windows Media Center:

"Files needed to play the video file are missing or not working correctly.
Please restart Media Center or the computer."

I can successfully play the exact same file natively in PowerDVD or WinDVD9.
Is this a CODEC problem or some sort? Any assistance would be most
appreciated.

Thanks,
John

Windows Vista Ultimate 64-bit with all updates