This is common with copy DVD's - It means that the disk has not been burnt 'carefully' - if you got it off ebay, it will have been burnt at max speed on cheap DVD's to maximise the profit the seller can make.

I suggest you do the following (if you can).

1) Use UltraISO to extract the DVD as an image on your PC.
2) Use something like Alcohol120% to re-burn the image on a decent quality DVD-R at the slowest speed your burner can manage.

Of course, the DVD copy you have may be no good and therefore cannot be extracted without errors - if that's the case, then i'm afraid you have a dud.

Hope this helps.