title: System.Net.HttpListenerException: Failed to listen on prefix 'http://localhost:8080
body: <p>I am running the following code from <a href="http://www.pluralsight.com/courses/aspdotnet-mvc5-fundamentals" rel="noreferrer">Scott Allen's ASP.Net Fundamentals course</a></p>
  
  <pre><code>using System;
  using Microsoft.Owin.Hosting;
  using Owin;
  
  namespace ConsoleApplication1
  {
      class Program
      {
          static void Main(string[] args)
          {
              string uri = "http://localhost:8080";
              using (WebApp.Start&lt;Startup&gt;(uri))
              {
                  Console.WriteLine("Started!");
                  Console.ReadKey();
                  Console.WriteLine("Stopping!");
              }
          }
      }
  
      public class Startup
      {
          public void Configuration(IAppBuilder app)
          {
              app.UseWelcomePage();
              //app.Run(
              //  ctx =&gt; ctx.Response.WriteAsync("Hello Owin!"));
          }
      }
  }
  </code></pre>
  
  <p>However when I run the console app I get a message</p>
  
  <pre><code>    Unhandled Exception: System.Reflection.TargetInvocationException: Exception has
  been thrown by the target of an invocation. ---&gt; System.Net.HttpListenerExceptio
  n: Failed to listen on prefix 'http://localhost:8080/' because it conflicts with
   an existing registration on the machine.
     at System.Net.HttpListener.AddAllPrefixes()
     at System.Net.HttpListener.Start()
     at Microsoft.Owin.Host.HttpListener.OwinHttpListener.Start(HttpListener liste
  ner, Func`2 appFunc, IList`1 addresses, IDictionary`2 capabilities, Func`2 logge
  rFactory)
     at Microsoft.Owin.Host.HttpListener.OwinServerFactory.Create(Func`2 app, IDic
  tionary`2 properties)
     --- End of inner exception stack trace ---
     at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments,
   Signature sig, Boolean constructor)
     at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Objec
  t[] parameters, Object[] arguments)
     at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invoke
  Attr, Binder binder, Object[] parameters, CultureInfo culture)
     at Microsoft.Owin.Hosting.ServerFactory.ServerFactoryAdapter.Create(IAppBuild
  er builder)
     at Microsoft.Owin.Hosting.Engine.HostingEngine.StartServer(StartContext conte
  xt)
     at Microsoft.Owin.Hosting.Engine.HostingEngine.Start(StartContext context)
     at Microsoft.Owin.Hosting.Starter.DirectHostingStarter.Start(StartOptions opt
  ions)
     at Microsoft.Owin.Hosting.Starter.HostingStarter.Start(StartOptions options)
     at Microsoft.Owin.Hosting.WebApp.StartImplementation(IServiceProvider service
  s, StartOptions options)
     at Microsoft.Owin.Hosting.WebApp.Start(StartOptions options)
     at Microsoft.Owin.Hosting.WebApp.Start[TStartup](StartOptions options)
     at Microsoft.Owin.Hosting.WebApp.Start[TStartup](String url)
     at ConsoleApplication1.Program.Main(String[] args) in e:\EShared\Dev2015\WebA
  ppScottAllen\ConsoleApplication1\ConsoleApplication1\Program.cs:line 12
  Press any key to continue . . .
  </code></pre>
  
  <p>I ran the Resource Monitor from the Task Manager Performance Tab and can see that there are 2 entries on Listening Ports for 8080. </p>
  
  <p>Both have Image=System, PID=4, IPv6 unspecified, Protocol TCP, Firewall Status Not allowed, not restricted</p>
  
  <p>I am new to Listening Ports, how do I get the code working?</p>