I keep getting random errors when I play this game its VERY annoying

[I'm a Cop, you Idiot]

Almost any map I try to play gives me this error http://steamcommunity.com/sharedfiles/filedetails/?id=121999546
if I try to load it once more I am able to play (only somethimes tho) this bothers me SO much because I have to face alot of loading screens and on top of that sometimes it just freezes for a second and then closes! no error message it just closes. and this one time I alt tabed and then opened the game again and when I did I was greeted with this message http://steamcommunity.com/sharedfiles/filedetails/?id=122003369
I was wondering if anyone had any solutions for these errors and im kinda serious so please dont just respond with witty sarcasm >_<

[Airik]

Go into 'tools' under 'view' at the top of Steam, install Left 4 Dead 2 Authoring Tools. If already installed, reinstall it. If that doesn't work, which it should, I would verifiy game cache in the L4D2 properties.