Internal server error in jquery /json webmethod

Here am calling a web method on click event. but am getting the error as inernal server error. here am calling this click event from dynamically created button . here i want to fire any one method.

page method is not firing.but ajax method is returning above error. in this page there r other 2 pagemethods r there. the other pagemethods r firing but this page method is not firing.

 <script type="text/javascript">
       $(document).ready(function () {
           $('#contaner_wrapper').css("height", "100%");
           $(document).on('click', '.fc-button-prev a span', function () {                
            //alert($("#calendar").fullCalendar('getView').start.toString());
               var abc = $("#calendar").fullCalendar('getView').start.toString();
               var ab = $("#calendar").fullCalendar('getView').end.toString();
//               PageMethods.EventDetails('E72', onSucess, onError);
//               PageMethods.Displaymonthevents('E72', onSucess, onError);
               $.ajax({
                   url: '/ViewEvents.aspx/Displaymonthevents',
                   type: 'POST',
                   data: 'hi',
                   contentType: 'application/json; charset=utf-8',
                   dataType: 'json',
                   async: false,
                   success: function (data) {
                       alert(data.d);
                   },
                   error: function (XMLHttpRequest, textStatus, errorThrown) {
                       alert(errorThrown);
                   }
                          });
               function OnSuccess(r) {
                    alert(r);
                   }
               function OnFailure(r) {
                   alert(r._message);
               }    
           });
           $(document).on('click', '.fc-button-next a span', function () {
               // Displaymonthevents();                 
               alert($("#calendar").fullCalendar('getView').start.toString());
               var abc = $("#calendar").fullCalendar('getView').start.toString();
               var ab = $("#calendar").fullCalendar('getView').end.toString();
               jQuery.ajax({
                   url: "ViewEvents.aspx/EventDetails",
                   type: "POST",
                   data: "hi",
                   contentType: "application/json; charset=utf-8",
                   dataType: "json",
                   success: function (data) {
                       alert(data.d);
                   }
               });
           });

           $(".fc-button-prev a span").trigger('click');
           $(".fc-button-next a span").trigger('click');
       });
         
    </script>

c#

 [System.Web.Services.WebMethod(EnableSession = true)]
        public static List<Events> Displaymonthevents(string eventdata1)
        {
            List<Events> events;

            BEvents obj = new BEvents();
            obj.ClubKey = (int)HttpContext.Current.Session["Ckey"];
            DataTable DT = obj.View();
{..........}
            return events;
        }