DVD backup problem with Pioneer 105

Hi, I have a Pioneer DVD-R 105 burner
and I brought 20 Princo 4X DVD-R when I first got my drive to try out, I copied some movies with them and they all worked fine on all my appliances, my xbox, Lite-on DVD Rom, The burner itself and both my Toshiba DVD players, I then thought well Ill buy another 20 and now all of these about 10 chapters in the xbox hates it, the liteon-dvd rom hates it and I get pauses on the toshiba dvd players and some artifacts on screen, I thought maybe the dye set of the DVD-R’s may have been dodgy so I took them back tot he shop and he said he hadnt had any other complaints but exchanged them for a new batch of princo’s again and suggested to check my firmware, I have the latest firmware and the just tried reburning and the same thing is happening ?? what now ??? anyone else had this problem ?? any help is appreciated thanks.