Have you tried a firmware update? Some of the early releases of the Sony and Pioneer clones had screwy firmwares that were the source of a lot of problems.
Know anyone who could burn you a copy on a -R to test? Your laser obviously is having a hard time reading the media. If cleaning/adjusting it doesn't help, you may need a more reliable media format. Or you might need to replace the laser unit
If it ain't broke don't try to fix it! But, hell if you can tweak that bastard just a little bit more....hehehe.