Read here and we can see that other people have both trouble and success running back ups on this device:
So... That tells us this device is finicky IE it requires a high quality burn.
DVD burners have varying levels of accuracy. To improve your burn:
-SLOW the burn speed for increased accuracy
-USE DVD-R only as it is the most compatible
-Use those Sony's DVD-r's at wal-mart or KMART because Sony makes DVR's and everyone else buys them from generic Taiwan manufacturer and relabel
I bet this will solve your problem. After you get a successful burn at 2x try 4x then 6 etc.