I had a similar problem with using a Kendo UI Grid with my MVC controller method.
Perhaps the problem is DateTime is an object, and JSON serialization converts it to an unreadable but de-serializable string. So the solution I had with my case is I converted the DateTime properties to string using the "ToString" method at the server method.
IEnumerable<Newsletters> ie = GetNewsletters();
//Selecting only part of the columns available, instead of the whole range returned by the GetNewsletters() function
IEnumerable<object> result = ie.Select(a => new
Title = a.Title,
Subtitle = a.Subtitle,
ShowAfter = a.CreateTime.ToString("dd/MM/yyyy") //If the property is a DateTime object, you MUST convert it to a string, otherwise it would not display properly
JsonResult jr = Json(result, JsonRequestBehavior.AllowGet);