Ok, this has happened to me before. I've the Collectors Edition, however I only have HL2 installed right now. While playing, the game will crash to the desktop and this message will pop-up: "Source - Fatal Error Could not acquire necessary game files because the connection to Steam servers was lost" I'm playing a single player game with no connection. It's the oddest thing, I've been playing like this for days, but at some point the game crashes like this and after that I cannot even enter the game anymore. So does anyone have a solution for this? Or at least what could be the source of the error? Thanks.