I have beaten A40 for the 2nd time, i even have the trophy on my PSN Account.
Yet when i select cheats it says "Beat the Game to Unlock Cheats"
Anyone else have this problem?
That's a bizarre problem, not one I've encountered, but do you have the latest update for the game?
Yes i do
Its really annoying me because as im sure you know
That Grivelnox is a pain in the /REDACTED/ to beat in Single Player
Well, my first suggestion would be to play the very last level through again, complete it then leave the cinematics and credits to run through.
Otherwise I'd recommend deleting the game data, not the save data, then the game will reinstall itself next time you start it.
EDIT:
Just found some more info at http://www.gamefaqs.com/ps3/605254-ratchet-and-clank-all-4-one/answers?qid=304462
Did you go through the game with just one character?
Yes i did and that was Nefarious
In which case I assume you got the skill point 'Master of Evil' if not then you've somehow missed a section and need to play that. I don't think you get the cheats unless you get one of the four character skill points. (Son of Kaden, Son of Orvus, Master of Evil, Hail to the Chief)
Otherwise it's delete the game data and reinstall the game. You'll find the game data under XMB->Game->Game Data-> All 4 One. Delete that file, you won't lose your progress or save data, then re-load the game.
If not then I'm stumped. 
Nope I unlocked plenty of cheats,maybe its a glitch