i was going to say turn on the dvd9 support but you have already done that, the only thing i can suggest is to check the disc for any scratches, ps2 lasers are very sensitive, i had a resident evil outbreak disc that used to freeze all the time and i professionally cleaned it and it still froze, also because the ps2 laser is so old now i think it will have a hard time playing dual layered games especially if you play a lot of burnt games on it.
i would also suggest you update the modchips firmware if you have a clone then be very careful with what update you use because it will fry your modchip and render it useless.
there is also another alternative, rip the disc to your computer and rebuild the iso for dvd 5 there are still a few guides out there that show you how to do this so try that if all else fails and good luck, hope this all helped.
PS3 Slim v3.55.4 CFW Rebug 1TB Internal, External 2TB
XBOX 1 with XBMC
Wii 3.2E + Cfg UsbLoader External 1TB
DS lite & DSiXL + Cyclo ds 8gb micro sd DStwo 16gb micro gd
PS2 V14 legit matrix infinity modchip
PSP slim 2006 5.00 M33-6 8gb memory stick pro duo
PSPgo with 16GB M2 6.60 PRO B10