I got the CSO file onto my ISO folder, but whenever I try to start the game, it keeps saying, "The game could not be started 80020321". Can anyone help me with this problem..

I need more information, what firmware are you running?

And what ISO loading settings are you on? If you've never heard of Recovery Mode before, or never accessed it before, you're probably in UMD-mode, you need a UMD inside the drive to play it.

Yeah, to fool the PSP that it plays a UMD game FROM the memory card.

I've had no time to downgrade my PSP. Too busy...

I use the Official Sony ISO loader to play the games, no UMD required and it works perfectly.

What's a CSO file and why is it in an ISO folder?

CSOs are compressed ISOs.

Ah, I see the problem. I switched the ISO mode to M33 Driver, and now it works fine.

Read the rules, fuckers.