I bought 8 gb Sony memory stick. I formatted it 3 times (twice with psp and one with windows) but still it doesn't work well. I put about 15 isos on it but it shows on my PSP only 3 ond one of them don't work! Is it Firmware foult or memory card? Beside PSP it works perfectlly. Right now I have 3.80 -m33 and Slim PSP. Maybe should I update to 3.90?