Error: System.Net.Sockets.SocketException: Unknown host. In asp.net

Dear, along with saying hello I wanted to ask the following question to the problem that came up:

I happen to be doing some tests to work with SignalR, in which the results are successful when I do the tests on localhost, but when I publish to the production server, I get the following error:

Unknown host System.Net.Sockets.SocketException: Unknown host

The way I started was the following:

First download the signalR packets

Then create the Startup file:

using System;
using System.Threading.Tasks;
using Microsoft.Owin;
using Owin;

[assembly: OwinStartup(typeof(MvcMasterPrueba.Startup))]

namespace MvcMasterPrueba
{
   public class Startup
   {
    public void Configuration(IAppBuilder app)
    {
        //ConfigureAuth(app);
        app.MapSignalR();
    }
  }
}

hub file:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using Microsoft.AspNet.SignalR;

namespace MvcMasterPrueba
{
public class MyHub : Hub
{
    public void Send(string name, string message)
    {
        Clients.All.broadcastMessage(name, message);
    }

    public void BroadcastMessageToAll(string nombreImpresora, String divHTML)
    {
        //Clients.All.newMessageReceived(message);
        Clients.All.imprimeDiv(nombreImpresora, divHTML);

    }
    public void BroadcastMessageToPrinter(string nombreImpresora, String divHTML)
    {
        Clients.All.imprimeDiv(nombreImpresora, divHTML);
    }

    public void JoinAGroup(string group)
    {
        Groups.Add(Context.ConnectionId, group);
    }

    public void RemoveFromAGroup(string group)
    {
        Groups.Remove(Context.ConnectionId, group);
    }

  }
}

The strange thing that when publishing on the server, I get the error, I would greatly appreciate your help, if someone has any ideas, your opinion will be welcome. Thank you very much. Other important information, when trying to log me in, I get the error, that is to say in this part:

public ActionResult Acceder(string User, string Pass)
    {
        string estado = "0";
        string ip = "";
        string db = "";
        string user = "";
        string pass = "";
        string password = "";
        string sql = "SELECT ip,db,user,CONVERT(AES_DECRYPT('pass','1234444444') USING UTF8) AS pass,password " +
                     "FROM usuarios " +
                     "WHERE email='" + User + "' and password='" + Pass + "' limit 1";
        conexion.conectar();
        MySqlDataAdapter datos = new MySqlDataAdapter(sql, conexion.conlogin);
        conexion.cerrar();
        DataTable dt = new DataTable();
        datos.Fill(dt);
        foreach (DataRow row in dt.Rows)
        {
            ip = row[0].ToString();
            db = row[1].ToString();
            user = row[2].ToString();
            pass = row[3].ToString();
            password = row[4].ToString();
        }
        if (Pass == password)
        {
            Session["Session_User"] = User;
            Session["ip"] = ip;
            Session["db"] = db;
            Session["user"] = user;
            Session["pass"] = pass;
            estado = "1";
            Session["ss_nro_caja"] = obtieneNroCaja();
        }
        switch (estado)
        {
            case "0":
                ViewData["Mensaje"] = "Usuario o Password invalido..!!";
                return View("Login");
            case "1":
                FormsAuthentication.SetAuthCookie(User, false);
                return RedirectToAction("Home", "Acceso");
            default:
                return View("Login");
        }
    }

It is assumed that when I go in this part, the error happens:

    case "1":
                FormsAuthentication.SetAuthCookie(User, false);
                return RedirectToAction("Principal", "Acceso");