I'm in the small bunker in the first mission, trying to take out the driver. I must do it with chloroform, in order to not soil the uniform with blood. The problem is that I can't get near enough to use the chloroform. The guard turns around when I'm a meter behind him. I've tried crouching/crawling/standing, and going as slow as possible, but no luck. I also tried taking out a normal patrolling guard, but with the same result. I'm playing on expert difficulty, and I've installed the Enhancement addon. I don't know if I installed it correctly, but I'll find out once I find some banners.

What could be causing this? Could I have done something wrong while installing the mod, and messed up the files? Or is the expert difficulty hyper-sensitive to detection? I also gunned down a couple of soldiers in the beginning of the mission, could this raise awareness?