Read errors whilst burning

When burning from one dics to another i occasionally get “error reading source disc” or something along that line. I changed the dvd rom from another tower to my newer tower and that seemed to cure the problem but now occasionally i get the same fault come up. I am using Nero express to copy the discs (not sure what version) there are some marks on the discs that i’m trying to do but they copy fine through dvd shrink (although this is slightly more long winded) and was wondering whether the fault could be with the dvd roms or the Nero software (although i haven’t had this problem in the past) both dvd roms are over 3 years old.

Also what do others think of 1 click dvd copy5 and dvd43

and lastly can anybody explain how people get 2 films on one 4.7GB disc