i’m not sure, actually. it has been well over a year since i got the game and i don’t remember if i ever had to do that. from what sarno said about the error, i assumed there should not be any such message when you install the game. i’m only guessing that reinstalling it will help fix the problem.
edit: there’s also a comment at the top of the forum (highlighted in blue) saying to update your client if you’re having an issue. reinstalling is one way to do that, if you don’t see an update available in steam.