I bought a slim psp of ebay which has the 3.71 M33 firmware. I have downloaded worms2 and it is a CSO file. When I open my PSP folder in my computer it comes up with the folder PSP. When i go into that folder it comes up with the folders APP and SYSTEM. I created a new folder called GAME and put the cso file in there. HOwever when I try to load it it says corrupted file and will not play.