Error! The requested URL did not return JSON asp.net mvc

Hi,
 
I have been using Telerik controls, I was using server binding, but I have to use Ajax binding, that is not working properly, I am getting Error "Error! The requested URL did not return JSON asp.net mvc"
Following is the Code in My Controller

[GridAction]
        [Authorize(Roles = "Admin")]
        public ActionResult Edit(int id)
        {
            Contact model = _cService.getContact(id, applicationID);
            GetContactType();
            if (model != null)
                return View(new GridModel());
            else
            return View();
        }
 

        //
        // POST: /Contact/Edit/5
        [GridAction]
        [AcceptVerbs(HttpVerbs.Post)]
        public ActionResult Edit(int id, Contact model)
        {
            try
            {                         
                _cService.SaveContact(model, applicationID); 
                return RedirectToAction("Index");
            }
            catch
            {
                return Json(new GridModel());
            }
        }
        public virtual JsonResult GetParents()
        {
            return GetContactsByType(2);
        }
        public virtual JsonResult GetContactsByType(int? id)
        {
            List<contact> list;
            if (id.HasValue)
              list=  _cService.GetContactCollections(applicationID).Where(x => x.ContactTypeId == id.Value).ToList();
            else
                list = _cService.GetContactCollections(applicationID).ToList();
            return new JsonResult
            {
                Data = list,
                JsonRequestBehavior = JsonRequestBehavior.AllowGet, // you may or may not need this line, depending upon your server config
            };
        }</contact>

 
and following Code in my view

  @(Html.Telerik().Grid(Model)
        .Name("Contact")
              //  .ToolBar(commands => commands.Insert())
       .DataKeys(keys => keys.Add(c => c.Id))
        
        .DataBinding(dataBinding => 
        {
             
            dataBinding.Ajax()
            
            .Update("Edit", "Contact", new { mode = GridEditMode.InForm, type = GridButtonType.Text })
            .Delete("Delete", "Contact", new { mode = GridEditMode.InLine, type = GridButtonType.Text });
        })
                   
        .Columns(columns =>
        {
            columns.Command(commands =>
            {
                commands.Edit().ButtonType(GridButtonType.Text);
                commands.Delete().ButtonType(GridButtonType.Text);
            }).Width(180).Title("Manage");
          columns.Template(o=> @Html.ActionLink(o.LastName, "Details",new {id=o.Id})).Title("LastName").Width(130);
          columns.Bound(o => o.FirstName).Width(160);
          columns.Bound(o => o.Address).Width(110);
          columns.Bound(o => o.CellPhone).Width(110);
          columns.Bound(o => o.HomePhone).Width(110);
          
        })

What I can do this Error, this error arise using Alert box, I have tried Modifying telerik.grid.min.js I have removed the line that,then it does not shows me error but also does not work.
Can somebody please give me Some suggestions.
Thank You