I am getting same error that most of you are. For the record I was able to play all episodes of the walking dead without a problem a few months back and haven't played since, today I bought the 400 days dlc and tried to start the game for the first time in months and now I am getting this error. I don't know if its related or if some new update on my computer/steam is causing the problem.
What I've tried:
-Running game on offline mode
-Running as system admin
-Steam Properties Compatibility mode for both Vista and Windows 7 checked with admin privilege checked (all other settings unchecked)
-Contacting Steam support (They send me here)
-Disabling Norton Anti Virus and windows firewall.
-Verifying game cache
None of these worked. Please help!