I get an error when I harm any guard at mission 4 but only after I go to the Large Metal Structure (don't know what it is called). After I go there if I shoot someone with a sleeping bolt a regular bolt knock them out from behind anything my game will stop responding and give me an error saying like
Fatal Error
(Filename not found)
something something (Filename not found)
It just has a ton of (Filename not found) and some other things after that

Any help would be Greatly Appreciated