Can you try uninstalling the behavior shield completely ? You have to do it via Control Panel, choose avast - uninstall and when you get the avast! setup screen select change(not uninstall) and untick behavior shield. Restart the pc and try your game.

http://www.shrani.si/f/2/sW/2YVQEoS7/bs.png

EDIT: You can get the behavior shield back via the same method.