Adding AjaxControlToolkit.config file to ASP.NET project

I am trying to add a file - AjaxControlToolkit.config to the root of the application in ASP.NET and when i type in the first tag <ajaxControlToolkit> in that config file, it gives me an error saying the element is not declared.  I tried to build and rebuild the project but no luck. Do i need to declare something in the web.config. i added CombineScriptsHandler.axd in the web.config.
All the ajax controls work as expected when i run the project but i wanted to speed it up a bit by creating the ajaxControlToolkit.config file but i can`t.
Am i missing something?

Thanks for your reply