no mouse invert ??

I just want to do achievement guide, and me need to know how to get achievement Kill Wanderer. I hope on someone's help

As title states the quest you get in town to deliver letter to guy in blue house is bugged. I deliver the letter but when I try to turn it in I keep clicking "FInish Quest" but nothing happens.

This game will have Co-op Multiplayer in the Future ???

:)