Overriding the Default WCF REST 4.0 helppage

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WCF

REST

I've been trying to find a way to override the default WVF REST 4.0 helppage with my own one, and came across this post:

http://code.msdn.microsoft.com/WCF-Custom-Help-Page-6f5a90f0

I've been trying to use the same approach in an IIS hosted service using the following code:

namespace WcfHelpRestService
{
    public class Global : HttpApplication
    {
        void Application_Start(object sender, EventArgs e)
        {
            RegisterRoutes();
        }

        private void RegisterRoutes()
        {
            // Edit the base address of Service1 by replacing the 'Service1' string below
            var factory = new MyServiceHostFactory();

            RouteTable.Routes.Add(new ServiceRoute("Service1", factory, typeof(Service1)));
        }
    }
}

namespace WcfHelpRestService
{
    public class MyServiceHostFactory : WebServiceHostFactory
    {
        public MyServiceHostFactory ()
        {

        }
        protected override System.ServiceModel.ServiceHost CreateServiceHost(Type             serviceType, Uri[] baseAddresses)
        {
            return new MyServiceHost(serviceType, baseAddresses);
        }
    }
}

namespace WcfHelpRestService
{
    public class MyServiceHost : WebServiceHost
    {
        public MyServiceHost(Type serviceType, Uri[] baseAddresses): base(serviceType,  baseAddresses)
        {

        }
        public override void AddServiceEndpoint(System.ServiceModel.Description.ServiceEndpoint endpoint)
        {
            endpoint.Behaviors.Add(new HelpPageEndpointBehavior("ACME LLC"));
            base.AddServiceEndpoint(endpoint);
        }
    }
}

however I keep getting the error:

[AddressAlreadyInUseException: HTTP could not register URL http://+:51443/Service1/help/ because TCP port 51443 is being used by another application.]<br />
System.ServiceModel.Channels.SharedHttpTransportManager.OnOpen() +1106

not quite sure what I'm doing wrong, so any help would be greatly appreciated.

TIA

Søren