Plutonium

So basically I downloaded a cracked version of MW3 from fitgirl and it ran perfectly so I decided to download myself plutonium so I could play online. Everything worked fine untill I wanted to go back and play CO-OP survival, that's when game crashed and said ''missing steamapi.dll file''. I redowloaded the game again and it worked like before but when I linked it with plutonium it stopped again, any clues?