Market Place Purchase Won't Load World

Apologies if the above isn't correct but this is the first time I have had a problem.  My wife purchased Ultimate Dragons for our son via the marketplace.  When you go to create a world it loads for a while but then crashes back to the screen with Minecraft closed.  You then re-open the app and it goes back to the start of Minecraft.  He has purchased it on an Ipad (the latest version of Minecraft) and plays under the ThwartTomcat212 name.