Final Fantasy X-2 freezes?

[3sc0b4r]

I've got a PS 2 3004 modded with the Magic 3 chip, most games work alright on it, but for some reason FFX-2 keeps locking up. I had similar problems with Onimusha 1 and 2 already, which ocassionally froze during gameplay, but it wasn't a problem to play for some time.

I've already tried burning it with RecordNow MAX, according to the F.A.Q. of this board, and with Nero. The first copy only freezes before the boss fight for the 1st sphere, the second one works with that fight but sporadically freezes a few seconds to minutes after that scene.
The DVD-Rs I use are the same as for the games which work fine.

Since I sometimes have trouble with booting games, requiring 1-4 attempts until the game is recognized correctly, I was wondering whether the problem might be due to a dirty laser lens, on the other hand a lot of games work?