Left 4 Dead 2 Demo won't load.

[Marshtomp]

Whenever I open L4D2, it runs fine until I load the Parish. when it's fully loaded, the game just closes. No error message, no warning just LOL I CLOSE NOW.
Anyone else have this problem and might know how to fix it? I already sent a ticket to steam. And I tried Reinstalling the game too.

[Jinx]

Is your steam client up to date?

[Purplecat]

If you try reinstalling, you probably need to manually nuke the gamecache files (+ L4D2 demo folder in the commons folder). I had a problem where Steam would insist on that my demo was corrupted, yet wouldn't seemingly fix it even after trying to do reinstall in Steam. Removing all related files and let Steam install it from scratch helped.