Once the trainer is run it stops me from selecting perks in the main menu, and in game. It seems that once the trainer is run steam blocks it, saying "Unknown Steam error prevented access to this" that's all.
First I'll ask but im sure you don't, your not using in MP right?, Second this has to do with your steam not the trainer, try defraging, and verifying integrity(right click on game in library go to properties, local files). If that doesn't work uninstall and reinstall game. GL