I know that some people have been having trouble backing up Superman Returns. I too was having a similiar problem but managed to get it done.
I had just purchased the Superman Returns DVD and wanted to do a full backup. I have a dual-layer Sony DRX820U whic has been working great. I use DVD X Studio’s CloneDVD ver220.127.116.11, but I kept getting an error message as I was about to start the burning process. I then upgraded to CloneDVD 4, and it backed up the entire DL DVD including Titles, Menus and Movie without any problems.