This is a known issue because of Vista's overzealous permissions.
I managed to sort it (Vista 64), but I really can't remember how as it was a while ago.
I think it involved going into Services in the Admin Settings of Control Panel and then giving the TVersity service admin rights.
Sorry I can't remember enough to be more specific, but hopefully that'll give you a headstart to sorting it out!
what wrong with media centre + transcode 360?