I think you should try hellcat's recovery flasher to upgrade to the latest firmware

It always works for me[Lol i have tried 2 times]
Got this link from this site here:
sendspace.com/file/0nw28r
Just copy it to psp>>game folder and follow onscreen instructions.
This is the easiest way to upgrade!
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PS:This file has not been uploaded by me.I got the link from the post of a guy called zarz123 from this site.I take no responsibility if you mess up your psp.It did work fine for m