When does this happen : As of day 2 Steam update.
On which track did it happen : (Powerplant, Playground, ...) NA
How often does this happen : (Always, very often, occasionally, could not make it happen again) NA
How to replicate the steps (if reproducible) : Have AVG Antivirus software Free edition running while trying to play the game.
More details : Played last night on release day with no problems, but next day (date of this post) Steam seemed to update the client, and the game immediately stopped responding. Got a blank screen for a few secs followed by my antivirus throwing up a screen telling me there was a threat detected with the Grip.exe. Trying to restart the game led to Steam informing me that the .exe wasn't found (presumably removed by my AV software).
Your specs : NA, was working fine until this update.