Cant back up certain DVDs

Hello all,
I have backed up Star trek enterprise seasons 1 and 2 but that was about a year ago (I have backed up dvd’s since then). But now i cant back up STE season 4. I can get to writing of the dvd then Clone says media problem (WriteDVD 2 W2). I have also used dvdshrink and DVD Decrypter any ideas would be appreciated.

I am using a laptop with a dvd rom drive and a freecom external dvd writer with datawrite and samsung dvd discs.

Thanks in advance