My fwiend is too shy to ask but he gets the error message "bad inline model 84" when he tries to load any demo, then after a short pause, his game crashes to desktop without the hl2 crashing message. Verifying didn't help.
Does anyone know anything about this?
...Just to make sure, his multicore rendering is disabled in advanced video options right?
I found a bunch of dead ends on Google when searching with the key words you provided. Here's a list of forum threads I found. Your friend should email Valve and link to all these unsolved cases. It may be his only hope.
http://forums.tf2maps.net/showthread.php?t=5410
http://www.gamefaqs.com/boards/437678-team-fortress-2/49617116?page=1
http://forums.tf2maps.net/showthread.php?t=4166