So now apparently my Source SDK suddenly expresses a dislike for Team Fortress 2; I can change the "Current Game" to any other game, but it simply won't let me select TF2. Every time I select it, it automatically switches to Half-Life 2, but I can change the game to Portal, or Counter-Strike: Source, or any other game. Now I've tried re-installing the SDK and that's done no good, I've re-installed TF2 to no avail, and refreshing the SDK content and resetting the game configurations to default have done nothing. I'm stuck now. Can anyone suggest a solution? NOTE: Problem solved.