Both codes are working for me, which version of pj64 are you using?
Are you pressing 'L' as in your keyboards L or the letter assigned for the n64 controller's L (which by default is A on your keyboard) ? if that makes any sense
I have a problem with that cheat. I looked in the cheat section while I was play Super Mario 64 and the cheat for levitaion wasn't there. I remember seeing it yesterday. I don't know what happened.