It could be many things: bad rips, low quality discs (or you've just not found the type your Duo likes), your laser pots need adjusting, or the laser could be on its last leg. The only way to know which problem(s) you're having is to try something else, like ripping your own legitimate games using Turbo Rip (so you know they're 100% good rips), burning other brands of discs (650mb Taiyo Yudens maybe), attempt a pot adjustment, etc.