Nero DVD burning problem

I am backing up DVDs using DVD Shrink Beta 5.0 and Nero 6.0 (currently demo). The problem is that sometimes the burn is completely successful and sometimes despite it appearing successful I am left with a disc that my reader/burner reports it “sees” as a CD and I can not view any of the files on the disk. I am a newbie (of sorts) and any help would be greatly appreciated!