SignalR "signalr/hubs" giving 404 error

Try call RouteTable.Routes.MapHubs() before RouteConfig.RegisterRoutes(RouteTable.Routes) in Global.asax.cs if you use MVC 4. It works for me.

        RouteTable.Routes.MapHubs();
        RouteConfig.RegisterRoutes(RouteTable.Routes);

It could be that you haven't added a reference to SignalR.AspNet.dll. If I recall correctly it's responsible for adding the route to /signalr/hubs.

From the SignalR 1.0.0 RC2 there is a README in the packages folder that says the Hubs route must be manually established. :) Here is a snippet...

using System;
using System.Web;
using System.Web.Routing;

namespace MyWebApplication
{
    public class Global : System.Web.HttpApplication
    {
        public void Application_Start()
        {
            // Register the default hubs route: ~/signalr
            RouteTable.Routes.MapHubs();
        }
    }
}

In my case, the main reason of this 404 is hubs were not properly mapped. RouteTable.Routes.MapHubs(); is now obsolete. For mapping hubs you can create a startup class as below.

[assembly: OwinStartup(typeof(WebApplication1.Startup))]
namespace WebApplication1
{
    public class Startup
    {
        public void Configuration(IAppBuilder app)
        {
            // Any connection or hub wire up and configuration should go here
            app.MapSignalR();
        }
    }
}