New Post: Routes and 404 and IgnoreRoute in Global.asax

In my project I've added a few (http)handlers that return XML files. It all functions as expected, but when I turn on the Custom 404 page (in URL Configuration), the Composite 404 is handling the request and a 404 is thrown.

After some reading I was hoping this could be fixed with adding

routes.IgnoreRoute("xml/{*.pathInfo}")

to the Global.asax, but I get an eror:

'System.Web.Routing.RouteCollection' does not contain a definition for 'IgnoreRoute' and no extension method 'IgnoreRoute' accepting a first argument of type 'System.Web.Routing.RouteCollection'

How can I make sure the path /xml/.. is ignored by the 404