Yes on some of the newer games it doesint start without the correct version. The only game that NEEDS 2.0 is GTA (I think). All the other games you can start by tricking your PSP into thinking it has a newer version with a version changer. I have given up 1.5 for good and I am staying at 2.0. Now I can run more then half of all homebrew (with the 2.0 loader at http://fanjita.org/ ). Plus have all the new features of 2.0, and play GTA.
Bookmarks