Try running plutonium.exe as an administrator. If that doesn't work - add %localappdata%/plutonium as a folder exclusion in Windows defender. Maybe defender is blocking the download.

Can you screenshot your MW3 folder please?

@emilartzz Have you ran exclusions.bat from the instructions page?

@Snieex Hello - not at this time, no.

@Palikzou https://forum.plutonium.pw/topic/561/mapping-a-controller-to-iw5