For me...hmmm...I don't put any codes in blue. I put em all in white, and when I need it, turn em on with the music note.

From what I understand by making codes blue, they stay permanently unless you restart psp. So, click them blue, then click music note twice, then they're still on, even if the thing says off. For the white codes, you have to click the music button and make NitePR say that the cheats are on.

As for the knife code, you might be using a bad knife code. Find knife code v5, thats what I use and it works amazingly.

I hope this helped!