I have tried the Ammo and reload, and neither seem to work. Is it because I am online?
Delete trainer and all files in
Learn how to make your own Trainer Cleaner for the above paths Here. Link
Reboot PC to clear excess memory, get a fresh copy of latest trainer, run trainer as admin, read the instructions and try again. At times, a new game may be needed to resolve failed options if the data in your save file was altered. Use on a new game and test the option. If it now works, quit to main menu and load your save and try it again.
P.S. CHEAT HAPPENS does not support or condone the use of cheats in a multiplayer environment.
Game version does not match, game purchased on wrong platform, it patched, antivirus is blocking it, not using a legally obtained game...could be any of these. Need more info than just that.