This post has nothing to do with the acceleration toggle in the menu which doesnt work! Please dont delete it!

Horizontal aiming is not possible because I have a negative acceleration. Moving mouse fast = slow response in the game, Moving mouse slow=fast respone in the game.
Lots of people have this problem in the internet. Tested everything.(reinstalling, new mouse / razer deathadder, new/other/only windows driver for mouse, updated USB mainboard drivers and chipset (asus p8p67), tested around with ingame settings and config)