dvd-r/dvd+r trouble

Hello all. I got few dvd-r frm memorex (16x). And tried to burn few of anime on my hardisk. Unforunately it did not burn. Format of the files is mpeg-2.
I’m using nero ultra edition 6.6 and my dvd+-rw is a “philips dvd+-r dvd 8710”.
While the dvd+r works fine. Is there a specific reason why this is happening?
I could really use a feed back on this as i have about 28 of these left and would not wish to waste them.
and yes i know the difference between the 2. But techinically they both are dvdR’s and should play on most players. I have a philips magnavox ntse dvd player.
Thanks
Dax.

Check 4 the latest firmware of ur DVD burner.