So, if I am not mistaken, it sounds like you're running a pirated copy. That would be the first issue.
Not being preachy about being a pirate, but the fact that a game as popular as L4D2 has weak seeds should probably have told you something....namely that the copy was bad. Valve updates it fairly regularly, and one of the first things the game does is attempt to ping back to the home servers for patches.
I've heard a lot more failures than sucesses with torrents of this game.