I'm currently attempting to play a backup copy of MGS3 through ESR but with little luck. I tried using both an NTSC version and PAL version of the game (I have a PAL region console) thinking that might fix the issue, but no dice. I've patched the ISO using the ESRPATCHER and have tried using both DVDR+ and DVDR-. I also tried a non modified memory card, to no avail. I've also been having the same issue with Devil May Cry 1 and 3, but strangely when I tried Final Fantasy 10 it worked fine....
Backup games played through ESR won't recognise memory card
Backup games played through ESR won't recognise memory card