It tells you right after that. Restart to a point before you applied cheats or edited your save.
This also appears to me. The only code I used was to get 999,999 cash at the start of the game. I have just over 30 hours of gameplay, (it's not much, however, it's time I spent to play) and since I don't have the save before using the cheat. Would I have to start over? If this is the solution I prefer to give up playing. It was a good game.