Only other thing i can sugest is update to 5.00m33-6
Sorry have no other suggestions
Fairly Easy download official 5.00 update and rename the eboot to 500.pbp and place on the root of the mem stick
and copy this
download to Psp/game/update and run it (after extracting obviously) or use hellcat but still have to do last step to go from -4 to -6