You dont have to reformat your mem stick to use devhook, it works perfectly fine without it, but if it doesnt work, sometimes a reformat fixes that prob, but 1.50 was not meant to play 2.00+ games, it will always tell you that you have to upgrade cuz sony did that to try to make all the homebrew users upgrade their psp's, now since everyone that had 1.50 was patient, we now have devhook to emulate all higher firmwares ( except 2.80 ), you can have all the features of that firmware and play newer games from umd or iso's.

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