AddHub.cs

private async Task AddHub(string address)
{
    Trace.TraceInformation("AddHub: " + address);
    // create a connection to a hub
    var hubConnection = new HubConnection(address);
    hubConnection.Headers.Add("ORLEANS", "GRAIN");
    var hub = hubConnection.CreateHubProxy("playerHub");            
    await hubConnection.Start();
    hubs.Add(address, new Tuple<HubConnection, IHubProxy>(hubConnection, hub));
}

clientScript.js

$(document).ready(function () {
    var hub = $.connection.playerHub;

    hub.client.playerUpdate = function (message) {
        alert(message);
    }

    $.connection.hub.start().done(function () {
        alert('listening for messages');
        console.log("listening for messages");
    })
});

PlayerHub.cs

public class PlayerHub : Hub
{
    public void PlayerUpdate(string message)
    {
        Trace.TraceInformation("PlayerHub.PlayerUpdate");
        // Forward a single messages to all browsers
        Clients.Group("BROWSERS").playerUpdate(message);
    }

    public override System.Threading.Tasks.Task OnConnected()
    {
        Trace.TraceInformation("PlayerHub.OnConnected");
        if (Context.Headers.Get("ORLEANS") != "GRAIN")
        {
            // This connection does not have the GRAIN header, so it must be a browser
            // Therefore add this connection to the browser group
            Groups.Add(Context.ConnectionId, "BROWSERS");
        }
        return base.OnConnected();
    }
}

pushToClient.cs

PlayerHub hub = new PlayerHub();
hub.PlayerUpdate("BLAH!");
return "Hub should be tested";

SignalRerror.txt

{"Message":"An error has occurred.","ExceptionMessage":"Object reference not set to an instance of an object.","ExceptionType":"System.NullReferenceException","StackTrace":"   at Microsoft.AspNet.SignalR.Hubs.SignalProxy.TryInvokeMember(InvokeMemberBinder binder, Object[] args, Object& result)\r\n   at CallSite.Target(Closure , CallSite , Object , String )\r\n   
at System.Dynamic.UpdateDelegates.UpdateAndExecuteVoid2[T0,T1](CallSite site, T0 arg0, T1 arg1)\r\n   
at AdventureTerreWebRole.Controllers.GameOneController.<Get>d__0.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   

at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Threading.Tasks.TaskHelpersExtensions.<CastToObject>d__3`1.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()\r\n   at System.Web.Http.Controllers.ApiControllerActionInvoker.<InvokeActionAsyncCore>d__0.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()\r\n   at System.Web.Http.Controllers.ActionFilterResult.<ExecuteAsync>d__2.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()\r\n   at System.Web.Http.Dispatcher.HttpControllerDispatcher.<SendAsync>d__1.MoveNext()"}