Error in Telerik ASP.Net grid AJAX Delete
===

I have a simple Telerik ASP.Net grid with Ajax delete command.  The deleting works, however, the page displays an error, and doesn't update. 

I would also like to call custom JavaScript upon AJAX call return, but can't figure out where to put the code.

Here's the view: 

                    Html.Telerik()
                .Grid<ScenarioVm>(Model)
                .Name("scenarioGrid")
                .DataBinding(dataBinding => dataBinding.Ajax()
                            .Delete("Delete", "Scenario").Select("Index", "Scenario"))
                .DataKeys(keys => keys.Add(c => c.Id))
                .Columns(columns =>
                {
                    columns.Template(o => o.Name).Title("Scenario")
                        .FooterTemplate(@<text>Total @Model.Count() </text>);
                    columns.Bound(o => o.IsLocked);
                    columns.Bound(o => o.ContractMonth);
                    columns.Bound(o => o.CreateDate);
                    columns.Command(commands=>commands.Delete().ButtonType(GridButtonType.Image)).Title("Delete");
                }
                        )
                        .Sortable()
                        .Scrollable(scroll => scroll.Height(200))
                        .ClientEvents(events => events.OnDelete("onDelete"))
                        )


The Javascript that gets called before the AJAX call: 

    function onDelete(e) {
            // alert(e.dataItem.Name + ": on Delete: can delete set to " + e.dataItem.CanDelete);
            var scenario = e.dataItem;
            if (scenario.CanDelete == false) {
                alert("Can not delete " + e.dataItem.Name + ": there exists a solution!");
                return false;
            } else {
                $.blockUI({
                    css: {
                        border: 'none',
                        padding: '15px',
                        backgroundColor: '#000',
                        '-webkit-border-radius': '10px',
                        '-moz-border-radius': '10px',
                        opacity: .5,
                        color: '#fff'
                    }
                });
                return true;
            }
        }


Controller method: 

    [HttpPost]
        [GridAction]
        public ActionResult Delete(Scenario scenario)
        {
            Logger.Info("Delete scenario " + scenario);
            if (scenario == null)
            {
                return new EmptyResult();
            }
            try
            {
                _scenarioRepository.Delete(scenario);
                Logger.Info("Successfully deleted " + scenario);
            } catch(Exception e)
            {
                Logger.Error(scenario + e.Message, e);
                var result = new JsonResult
                {
                    JsonRequestBehavior = JsonRequestBehavior.DenyGet,
                    Data = new { ErrorCode = 1, ErrorMessage = e.GetType() + ": " + e.Message }
                };
                return result;
            }
            return new EmptyResult();
        }