Error System.Data.Entity.Infrastructure.DbUpdateConcurrencyException while doing update with entity

Good morning.

I need to do an update via entity and it accuses me of the following error:

System.Data.Entity.Infrastructure.DbUpdateConcurrencyException: 'Store update, insert, or delete statement affected an unexpected number of rows (0). Entities may have been modified or deleted since entities were loaded. 

controller code

 // GET: AreaClientes/Edit/5
        public ActionResult Edit(int? id)
        {
            if (id == null)
            {
                return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
            }
            Protocolo protocloLatam = db.Protocolos.Find(id);
            if (protocloLatam == null)
            {
                return HttpNotFound();
            }
            PopulaTipo(protocloLatam.Id);
            PopulaArea(protocloLatam.Id);
            PopulaClassificacao(protocloLatam.Id);
            PopulaAtividade(protocloLatam.Id);
            PopulaCidades(protocloLatam.Id);
            PopulaDestinatarios(protocloLatam.Id);



            // ViewBag.GAreaClienteId = new SelectList(db.GAreaClientes, "Id", "Descricao", areaCliente.GAreaClienteId);
            return PartialView(protocloLatam);
        }
[WebMethod]
        [ScriptMethod(UseHttpGet = true)]
        public JsonResult Editar() //[Bind(Include = "Id,Area,GAreaClienteId")] 
        {
            if (ModelState.IsValid)
            {
                Protocolo protocolo = new Protocolo();
                protocolo.ColaboradorId = int.Parse(Request.QueryString["IdColaborador"]);
                protocolo.DestinatarioId = int.Parse(Request.QueryString["DestinatarioId"]);
                protocolo.OrigemId = int.Parse(Request.QueryString["OrigemId"]);
                protocolo.ClassificacaoId = int.Parse(Request.QueryString["ClassificacaoId"]);
                protocolo.ContaContabilId = int.Parse(Request.QueryString["ContaContabilId"]);
                protocolo.AcaoSolicitaId = int.Parse(Request.QueryString["AcaoSolicitaId"]);

                db.Entry(protocolo).State = EntityState.Modified;
                db.SaveChanges();

                return Json(new { resultado = true});
            }
            else
            {
                IEnumerable<ModelError> erros = ModelState.Values.SelectMany(item => item.Errors);

                return Json(new { resultado = false, mensagem = erros });
            }
        }

ajax code that triggers the function

$("#btnEditar").on('click', function () {
    var erros = 0;
    $("div").find('*').each(function () {
        var classe = $(this).attr("class");
        if (classe !== undefined) {
            var numItems = $('.has-error').length;
            if (numItems > 0) {
                return false;
            }
            else {

                $.ajax({
                    type: 'GET',
                    url: 'ProtocoloLatam/Editar',
                    dataType: 'JSON',

                    data: {
                        IdColaborador: $("#lblColaborador").attr("data-idColaborador"),
                        DestinatarioId: $("#ColaboradorId").val(),
                        OrigemId: $("#OrigemId").val(),
                        ClassificacaoId: $("#ClassificacaoId").val(),
                        ContaContabilId: $("#ContaContabilId").val(),
                        AcaoSolicitaId: $("#AcaoSolicitaId").val(),
                    }, success: function (data) {

                        $("#minhaModal").modal('hide');

                    }
                }).done(function () {
                    toastr.success("Editado com sucesso.");
                    setTimeout(4000);
                    window.location.reload();
                });
                return false;

            }
        }

    });
});