Plutonium

your problem is just like me just copy this file and paste it in your mw3 game folder just make sure you have a copy of it somewhere if it disapears next time cuz mine disapears when ever i start a new mw3 game and make sure you update your plutonium alright?😁
https://mega.nz/file/DjAgxLaQ#x6I2tB69TW-y78IT50K3ljR_27O_PPa6B8N3mtvWFdQ

That means you didn't select a folder that contains the mw3 game files.