I managed to craft Emerald dragon on 15 Feb 2013 on my a1pro Dragon Story mobile entertainment app game.
The secret to crafting an Emerald dragon is to use spare dragons with the colour element of Green, with several Yellow elements. These spare dragons are the by-products of your breeding programme. Like when you try to breed Diamond dragon and don't need multiple copies of dragons that are produced in the process.
Have you manged to craft your Emerald dragon?
If you are trying to craft Emerald dragon, good luck to you.