I just want to thank you also bjbinc - I'd spent half the night chasing my tail trying to fix my Media Center.
I'd installed the October Rollup for Media Center for Vista and everything had stopped working, after 30 seconds I got the good old 'A Critical Media Center Process has failed...' error and nothing worked.
I'd been crawling all over everywhere trying to find people having similar issues, I eventually tied down the error to ehRec from crawling through .crash files, found your post and bingo everything back to lovely perfection!
So a huge thank you from me because I would never have thought to do that! Cheers.