Jump####t,

The only thing I haven't unambiguously established in working this through logically is that the actual in your hand backup GT3 CD that works in your friend's machine is the one that doesn't work in yout PS2. If that is true, then I've exhausted the bounds of my knowledge.

If that is not true, i.e. the one you try to use is a copy of the one your friend uses, then have you tried the one your friend uses? Your posts are not entirely clear on this.

Best wishes