Nero Recode works, Burning ROM Doesn't?!

I am just in my first day of AnyDVD trial.
Using Nero Recode to copy DVDs works fine.

Yet with DVDs that fit on a single layer DVD+R, I should
also be able to copy using Nero Burning ROM?!
I don’t want the DVDs structure to change, so I’d prefer
that option.

Yet whenever I try it Nero Burning ROM ( just says
“This DVD cannot be copied”.

Any clues?

No, this should work just fine. Haven’t tried Nero, but you can use any 1:1 copier, e.g. CloneCD. You can even use CloneDVD’s third option “write existing data”.