Woah, hold on, 've encountered one more problem (p.s.: don't know if the updater fixes it, haven't tried yet:) )
My save games don't work in 5.50 GEN-D3 ! i tried erasing the save games on my memory stick and putting in the ones that i'd backed up, but the problem still remained.
I fixed the problem (guess how) by downgrading my PSP to 5.50 GEN-D2 again...
BTW, does anyone know a way to downgrade the PSP to 3.80/3.90 M33 ?? I tried simply putting the 3.90 M33 upgrader to ms0/PSP/Game and load it up on the PSP but it didn't work..