I am getting Failed to load resource: the server responded with a status of 500 (Internal Server Error) - intermittently in Knocout/MVC app

Question

Getting intermittent 500 internal server error while laoding page.

Client Side code to load Dropdown on Page whenever error occoured it is not hitting server side controller.

    // Perform initial load for data for screen
    self.loadData = function () {
       // debugger;
        //Set Current login userid
        var userElement = $('#currentUserID');
        var LoginUserID = parseInt(userElement[0].getAttribute("data-userid"));
        self.currentUserID(LoginUserID);


        // Load the refLocation_Lookup by calling the WebAPI
        lorapp.ajaxGet("/api/apirefLocation/GetForDDL", null,
            function (data) {
                var model = ko.mapping.fromJS(data);
                self.refLocation_Lookup(model.RetData());
                //load category data for working out the path
                self.loadCategoryData();

                // Load the refDeliveryOptions_Lookup by calling the WebAPI
                lorapp.ajaxGet("/api/apirefDeliveryOptions/GetForDDL", null,
                function (data) {
                    var model = ko.mapping.fromJS(data);
                    self.refDeliveryOptions_Lookup(model.RetData());
                    //// Load the item condition by calling the WebAPI
                    lorapp.ajaxGet(baseItemConditionHelpAPIUrl + "/GetForDDL", null,
                           function (data) {
                               var model = ko.mapping.fromJS(data);
                               self.refItemCondition_Lookup(model.RetData());
                               // self.getItems();
                               //// Load the condition help calling the WebAPI
                               lorapp.ajaxGet(baseItemConditionHelpAPIUrl + "/GetForTooltip", null,
                               function (data) {
                                   var model = ko.mapping.fromJS(data);
                                   self.conditionHelp(model.RetData())
                                   self.getItems();
                               },
                               function (response, json) {
                                   toastr.error("refItemConditionToolTip: " + (json ? json.Message :               response));
                               });
                           },
                           function (response, json) {
                               toastr.error("refItemCondition_Lookup: " + (json ? json.Message : response));
                           });
                },
                 function (response, json) {
                     toastr.error("getrefDeliveryOptions_Lookup: " + (json ? json.Message : response));
                 });
            },
            function (response, json) {
                toastr.error("getrefLocation_Lookup: " + (json ? json.Message : response));
            });
    };

---

Ajax Call

lorapp.ajaxGet = function (url, data, successCallback, errorCallback, isBusyCallback) { ajaxCall(url, data, 'GET', successCallback, errorCallback, isBusyCallback); };

  function ajaxCall(url, data, httpVerb, successCallback, errorCallback, isBusyCallback) {
        if (isBusyCallback) {
            isBusyCallback(true);
        }

        $.ajax(url, {
            data: data,
            type: httpVerb,
            dataType: 'json',
            contentType: 'application/json',
            success: function (response, textStatus) {
                handleSuccess(response, textStatus, successCallback, isBusyCallback);
            },
            error: function (xhr, textStatus, errorThrown) {
               handleError(xhr, textStatus, errorThrown, errorCallback, isBusyCallback);
         }
        });
    }

Why Intermitenat 500 error -