Plutonium

Hello, I've wanted to play some private multiplayer matches against bots in MW3 for a while now, but with the update the game had a few weeks ago, I haven't been able to anymore

I investigated the problem and saw that the game needed to be downgrade, which I did and the game started, but when I try to start a private match, I get this message

Hey Vipadus, what files did you use to do the downgrade?
Could you please write the download codes?
I'm new to this and don't know much about it, I just want to play and have fun