I have also encountered this problem, after the update thought it might have been server specific (i occasionally run on modded servers) till i did a hard reinstall of Arma 3 and even in vanilla editor i still couldn't look around with the mouse.

Mouse itself was working, as in buttons were operating fine left click still fired primary weapon, right click still did zoom, middle mouse still operated the action menu, mouse worked in menus fine, and mouse worked fine in vehicles, but it's as if it wasn't recognizing "mouse up,left,down,right" for the "aim up,left,down,right" commands.

Not a device issue as far as i can tell, binding the aim functions to a joystick works but aiming your rifle with a joystick is just... cumbersome. TrackIR seems to be unaffected.

Your 'workaround' of bumping back to the pre 1.4 legacy did work, but of course now i can't connect to any of my regular servers because of incompatible version.

Take a look into your controls and go to the view settings (Configure->Controls->View). Is your mouse assigned to "Aim Up", "Aim Down", "Aim Left", "Aim Right", "Look Up", "Look Down", "Look Left" and "Look Right"? If not, there is your problem.

I too am having the same problem, using Logitech G400. I can navigate every menu with no issues but when I login and start multiplayer into my group's server I cannot move my character with my mouse. I can shoot, aim down the sights and zoom in but no matter how much I move my mouse. My character will not turn.

Tried it with defaulting controls, revalidating arma 3 and turning off the logitech software.

All with no avail.

@Koala,

jo, try this settings and it works !!!

but why that settings are gone ?
i dident have them before because i use track IR for look around
and not need it for the mouse...

aim up/down/left/right still has that setting but without movement...

i think that is not normally and is an issue of the update...

but thanx for the tip/trick i will use it until next patch ;)

@ Koala

THIS DOES WORK. However... i did some testing

I completely unbound aim up,left,right,down, and bound the mouse to ONLY look up,left,right,down, and it does the aiming.

before, i had look unbound (because track IR) and aiming bound to mouse.

So, as of 1.4, the aim functions apparently do nothing at all, and the aim functionality is now under "look".

At least we have a working solution, but still a bug of why are there useless/misnamed functions?

The developers somewhere talked something about hardcoded key assignments before 1.40 and recommend, to check (and maybe default) the controls if someone has some trouble with his individual assignments.

Glad I could help you guys.

Last update broke middle mouse button for me. Reset controls to default was no help.