Plutonium

Same here. The plutonium IW5 window crashes when trying to apply the settings and seemingly hijacks the mouse input. Keyboard input still works so I just alt f4'd the console to kill it. I edited the plutonium.cfg config file in C:\Program Files (x86)\Steam\steamapps\common\Call of Duty Modern Warfare 3\players2 and set the line with r_displayRefresh to seta r_displayRefresh "144 Hz" instead, that seems to work.

Xerxes I do know what i'm talking about... but, I was adding onto the discussion on when the error also occurs. Maybe if you looked around just a bit harder, you would see that the thread I replied to was about the error and I talked about how it's not the origin of the issue but rather another way to reproduce the issue.

Repair your game files, follow this guide.

Please never ever touch the base game files, if a tutorial instructs you to do that it is written by an ape. IWD files are just zip files and you can create your own ones that contain all files of one mod which also helps to organize them.