when i was messing around with custom gameboots i found that normal "game" pmf files work fine on devhook custom firmware (not tried on 1.50) and when it came to converted pmf clips devhook would not work (just show a white screen with PSP logo) and custom firmware would work with anything i threw at it even a 1.6mb "360" startup screen (note it only plays 1.5ish seconds then loads the game).

p.s. what firmware are you using (is it devhook), what flashing method are you using and have you got enough space on flash0.

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