This can happen onvarious reasons:
1 ) dvd media is dirty - you can try to clan it
2 ) dvd media is damaged , you have to replace it
3 ) your drive is a region locked rpc2 drive, which does not allow reading of scrambled sectors from a different region and try to read a dvd from a different region.
You can try to find a rpc1 patched firmware at www.rpc1.com
4) your drive is an rpc2 drive that has not yet been assigned a region. try to assign one, or try to find a rpc1 patched firmware.
Plus the more you back up a back up the less the quality gets.
Why are you doing it that way? Just get the original and back it up again.