help with psx back up

I can copy most psx games using nero v5 but can anyone tell me why when some of them have copied, they wont play? they will maybe get to the loading screen and then stop loading. Is it that i need to patch some games or is there another way to do it. I live in the uk so they are pal versions of the games.Some of the games i,ve had problems with are final fantasy viiii, crash bash, need for speed-porche. Any help would be greatly appreciated. My email address is dazzlowe**********com if anyone wants to email me. thanx.