As getit29 said the label causes the dvd to warp when the label gets older it shrinks, resulting in problem reads because of the warp. You can remove the label by applying wd-40, yes wd-40 let it soak and the label will come off. Once clean you can then make a copy of the dvd. Paper labels are a big no when it comes to dvd’s.
Most users in this forum will tell you to get a cd/dvd printer. I’ve gotten a Epson r300 for $59 at Fry’s. Get Taiyo Yuden or Verbatim printable disks and you set.