Two things I've been told but yet to try, as I can't get the disc back off the mate I lent it to (hence the need for a backup, I don't like lending out valuable discs!).
Burning at 1x may help, as a friend says he can't burn any PS2 games at 4x on his Pioneer writer, they just don't work.
A program called DVD Xcopy Express Platinum, which can apparently copy DVD discs as mirror images, will burn most 'tricky' PS2 backups.
I'll feed back when I've tried both these methods
