My Memory Stick is defective and corrupts files, that was my problem Funny it works like a charm in SE W810i or K750i . But when I throw some mp3's or iso's on it while in the PSP it shows 3Mb/s writing speed and from 90 mp3's only 18 worked and not even one iso worked! 10x USB2.0 On good old USB1.1 there's no problem but it's very very slow ;(
My w810i is a lot more pickey when it comes to my fake Memmorysticks
It does not save photos in the highest resolution to them
(i guess they are to slow)
but my PSP loads Isos just fine from them...
if you copy files via the usb 1.1 to your MS are they readable afterwards?
For me the PSP is my most trusty card reader (my cheap 16/1 reader corupts files sometimes and the w810i only works as usb 1.1 device)
at the moment i belive your Memmorystick slot in the PSP is broken o.O