Can't copy dvd's I've already burnt

I have a strange problem whenever I burn a copy of a dvd (ie a copy of a copy) using nero copy dvd to dvd the disc burns fine with no errors but won’t play in a standalone dvd player or pc it’s not the media because I have tried it on various types of media including dvd-rw and I get the same problem the only way I can get a succesful copy that plays is to run the disc through dvd shrink again and it burns perfectly the burner is a pioneer 111D it will burn dvd’s when I’m using VSO Convert x it will also burn data dvd/cd, audio cd’s the only problem is with copying dvd’s

Windows XP PRO SP2

Nero 6.6.0.16
Nero 3.1.0.16http://club.cdfreaks.com/newthread.php?do=newthread&f=48#
Confused