i ran the program on all my disks and they all say 'error! unrecovered read error (031100). it occurs towards the end of the dvd. what exactly does this mean and how do i prevent it? i am able to play ok w/ all these dvds

also i am using dvdshrink + nero to burn, how do i control it and make it burn at 1x (i can make it 4x or 2x)