Hi guys. I've got a problem I can't figure out despite reading several threads on this great site.

I recently bought a psp 2000 with 500 m-33 custom firmware.
I then attempted to play an ISO I downloaded, specifically Valkyria Chronicles 3.
I can see the game on the memory stick and start it, but then I get an error message
I eventually found this site.
I have tried switching between m33 no disk and sony no disk modes.
I upgraded to 550 gen d
I then tried the ISO tool 1.51v2 fix
I will try some other games as I download them, but so far no luck with this one.
Any suggestions will be appreciated.