To backup a backup ON THE FLY for testings purposes only since your allowed to make only one from the original is simple.
You must have a LG "8161B" DVD-ROM, you can use with ease Nero Express with any Pioneer DVD-R on the fly without any errors or the extra padding that almost ALL other DVD-ROMS LG models and not will do, by extra padding i mean if the original backup DVD occupies only half of the DVD the LG "8161B" DVD-ROM will make a copy with the exact size, on the other hand if you use any LG "8160B" and under or any other branded DVD-ROM reader(at least all of the ones i've tried) these will make the Pioneer DVD-R(all models) write to the end of the disk thus the Extra Padding will
occur and at the break point(end sectors of the original) you'll get either an error or the xtra padding.
P.S. Usually the problems that most users are having has nothing to do with Dvd2one or any other replicating software thats out there it's a bad hardware combination just do the above and all of your problems are over for Dvd Movie's, Ps2's(the pickiest) and Xbox backup's and i repeat you must record on the fly no more then 1X if you want zero coasters!