Looks like I've found our problem. I found this Sticky in the General Discussion forum;
I see many people having problems when ripping their PSX CDs
Some games, including the Final Fantasy games, Formula One games, etc, have a copy protection, so once you've ripped your own CDs, you must patch you iso or you'll just get a black screen.
So after ripping your games, if your iso doesn't work with FpseCE or Fpse for Droid, please have a look there, to verify that a "protection fix" is not required:http://consolecopyworld.com/psx/psx_patches.shtml