Same problem except I burned on Imgburn at 2x on a memorex -r. I'm guessing (or hoping) that it's the media. I've heard Verbatim is the best. I've backed up several games. I have this problem with MarioKart and Pokemon Battle Revolutions. Mario Party 8 and Wario Land Shake it run a little slow (but mainly on load screens or story screens.) I'm gonna keep the iso's till I get some Verbatim.
Any help would be appreciated.