The code may only work in certain parts of the game, if you're certain you're in the right part, then open nitePR and press "R" until you're at the options page, go down to CheatHZ and press right on the dpad so it's at 15/1000. this makes your codes repeat to ensure that they're on.

As for freezing, I've never frozen just for having nitePR, only time I freeze is if I have a bad code on or on at the wrong time.