Marvel vs capcom 2 won't play on ps2 slim

[mas]

So I have a ps2 slim that plays blue disc, dvd's, psone, and ps2 dvd games no problem. For some unknown reason the ps2 slim will not play marvel vs capcom 2. It plays everything thelse but that game.
So I got a white ps2 slim from a co worker and a bunch of games and the same thing happens. It won't read the mvc2 disc at all. But for some reason I have a crappy fat ps2 that won't play any games but when it stands up and it plays mvc2 just fine.
Does anyone have any thoughts or ideas on this? Also my disc is in prestine shape

[d123456]

Long shot, but the disc is from a different region
and the phat is either modded or from that same region
Could be that the disc is damaged or warped, but that the good old phat's laser can still read it.
I cannot imagine an incompatibility with the slim.