Intermittent "necessary files not installed or are corrupt" error when trying to play .dvr-ms files

I get this error occasionally when trying to play recorded TV files (dvr-ms)

in VMC, and the suggested restarting/rebooting doesn't help. My only

recourse is to restore a disc image made when things were working correctly.

I mainly use TheaterTek or ZoomPlayer for multimedia files and sometimes

need to use GraphEdit to analyze/create playback graphs. Is it possible that

this experimentation with filters/renderers, etc. (which sometimes causes

GraphEdit to crash) corrupts the default graph that Vista uses? Is there any

way to troubleshoot this? VMC error messages are so vague, it's hard to tell

exactly what is going on (Event Viewer, as far as I can tell, isn't much

help either).