I complied iso2opl on my Mac with no errors (thanks to jimmi's suggestion). It was actually simpler than I thought.
Works great! I tested it with Socom 3, which is over 4GB, with no problems.
I can post mine so you can compare to yours to see if it was your iso or not.
I don't think there is a need for that until someone else confirms this problem. I've tried with about 10 ISOs of mine and this one is the only one having a problem, so it's probably my rip that is at fault. Since I'm quite busy, I won't make further tests that will probably include re-ripping the game unless proved necessary...