Pls Help - cannot get copy of DVD to work on DVD player

I have an Intel HT PC with Windows XP. It has a CD/DVD Reader and
writer. It is fairly new.

I was trying to make a copy a DVD.

After copying the DVD will not work on a DVD player.
It says "cannot play"

However the copied DVD will work on the same PC as well as on another
PC.
Why is that ?

I have used both an erasable DVD as well as a Non erasable DVD. Both do
not work on DVD players.

Can anyone pls help ?

I am not Technical so pls explain in more detail for folks like me.
Thanks'
Ava