I need help with my psp, which I just recently modified. ISO games don't load.?

So yea, I hacked my psp 2001; downgraded to 5.00 m33-4. And I stored on the memory stick some games, the ones on CSO format load perfectly, but the ISO don't load at all and it gives me an error saying "The game could not be started. (80020148)". Can anybody help me out with this?