I know this is going slightly off topic but do you know when people try to trick the psp into updating (well downgrading) by loading a memory card with a new update then swaping the memory card with a different one with for example 1.5fw is because the memory card slot has a switch kind of thing so the psp detects that the memory card has been removed. So if the switch (if one exists, this is just my theory) is held down some how and the memory card is switched it should work.

Hopefully that made sense!!!