Log me correctly on asp.net

I'm starting to work with webForms / aspx, I'm trying to implement a simple log but there is an error in what I'm trying to do.

I have this code in the backend that if the user is incorrect it returns a response value to AJAX to show an alert, if the user is correct, it adds a session variable and the redirection is done from AJAX

[WebMethod]
public static string buscarUser(string name, string pass)
{
     SqlDataReader rd;
     string resp = "";

     using (SqlConnection cnn = new SqlConnection("Data Source=ALPHA- 
     2MYT322;Initial Catalog=Ejemplo1Login;Integrated Security=True"))
     {
            SqlCommand cmd = cnn.CreateCommand();
            cmd.CommandText = "EXEC login @nn,@pp";
            cmd.Parameters.Add("@nn", SqlDbType.VarChar, 50).Value = name;
            cmd.Parameters.Add("@pp", SqlDbType.VarChar, 200).Value = pass;

            cnn.Open();
            rd = cmd.ExecuteReader();
            if (rd.HasRows) //Si el dataReader contiene filas es que existe un usuario
            {
                 while (rd.Read()) //Lee
                 {
                     HttpContext.Current.Session["nombre"]=
                     rd["nameUser"].ToString();
                     resp = "SI";
                  }  

             }
             else
             {
                  resp = "no";
             }

         }


      return resp;
    }

On the page to which I point I put this in the Load

protected void Page_Load(object sender, EventArgs e)
{
    if (Session["nombre"] == null)
     {
         Response.Redirect("Login.aspx");
     }
}

But every time I have a successful login (so the user exists), it redirects me to the page but it shows me this:

What should I add or remove in order to log in correctly?