First of all, welcome to the forum.
Usually problems like these are due to a bad media. Try to post a scan of these media.
To do a scan, download latest version of CD-DVD speed.
Then start cd-dvd speed (don't require installation), insert your faulty DVD. and click on Disc quality tab. Select 4x as scan speed, and wait until finish. Finally, press on the little button on upper-right of the window (the button with a little floppy disc) and save the image in png format.
Finally, post the image on this thread