OWIN HttpListener not located

When I try to start :

WebApp.Start<SrvcHst>(new StartOptions { Port = 9956, 
     ServerFactory = "Microsoft.Owin.Host.HttpListener" });

I get the following exception. What could be the root cause?

System.MissingMemberException was caught
  HResult=-2146233070
  Message=The server factory could not be located for the given input: Microsoft.Owin.Host.HttpListener
  Source=Microsoft.Owin.Hosting
  StackTrace:
       at Microsoft.Owin.Hosting.Engine.HostingEngine.ResolveServerFactory(StartContext context)
       at Microsoft.Owin.Hosting.Engine.HostingEngine.Start(StartContext context)
       at Microsoft.Owin.Hosting.Starter.DirectHostingStarter.Start(StartOptions options)
       at Microsoft.Owin.Hosting.Starter.HostingStarter.Start(StartOptions options)
       at Microsoft.Owin.Hosting.WebApp.StartImplementation(IServiceProvider services, StartOptions options)
       at Microsoft.Owin.Hosting.WebApp.Start(StartOptions options)
       at Microsoft.Owin.Hosting.WebApp.Start[TStartup](StartOptions options)