Child actions are not allowed to perform redirect actions. MVC 5

On my homepage, there is a shortcut button that opens a modal, and within that modal it has a partialView that points to an action within another controller . Until then calm down.

<div class="modal fade" id="modalCreate" tabindex="-1" role="dialog" aria-labelledby="createClasseModal">
        <div class="modal-dialog" role="document">
            <div class="modal-content">
                <div class="modal-body">
                   @Html.Action("Create","Classes")
                </div>
                <div class="modal-footer">
                    <button type="button" class="btn btn-default" data-dismiss="modal">Cancelar</button>
                </div>
            </div>
        </div>
    </div> 

When opening the modal with partial view being displayed correctly for inclusion of the information. After the inclusion, the routine executes savechanges correctly in controller , then it gives RedirectToAction to return to the home screen.

 [HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult Create([Bind(Include = "id,descricao,dia_1,dia_2,horario,dt_inicio,dt_termino,sala,limite_max,limite_min,preco,status,professor")] Classe classe)
    {
        ViewBag.professor = new SelectList(db.Pessoa, "id", "nome", classe.professor);
        if (ModelState.IsValid)
        {
            db.Classe.Add(classe);
            db.SaveChanges();
            return RedirectToAction("Index");

        }

        return View(classe);
    }

In debug it returns to index , and at the moment of redrawing the screen with modal, it accuses the error:

Does anyone have any ideas for fixing this?