You have the wrong software to duplicate said DVD.
In closing, a DVD can't be overwritten. Maybe you meant some DVD-RW or DVD+RW or even a DVD-RAM disk, but be careful about how you write this this ... DVDs as media are not recordable.
Would want to learn how to burn a DVD, I'm using Nero Express 6. I have a CD-RW and just install a DVD-RW+. When I pop my DVD in to the DVD Drive, and click copy entire disc. It give me a message that I can't burn it b/c there some kind of protection. Please show me how can I make it work.