error while creating datalist using jquery

See more:

C#

ASP.NET

jQuery

JSON

function FillGrid() {
            debugger;
            var options;
                var data = { };
            var json_data = JSON.stringify(data);
            $.ajax({
                type: "POST",
                contentType: "application/json; charset=utf-8",
                url: "D2-1-1main.aspx/FillGridView",
                data: json_data,
                dataType: "json",
                success: function (data) {
                    $("[id*=dlCustomers]").attr("border", "1");
                    var row = $("[id*=dlCustomers] tr:last-child").clone(true);
                    $("[id*=dlCustomers] tr:last-child").remove();
                    $.each(data.d, function (key, value) {
                       
                        var customer = $(this);
                        $(".CustomerID", row).html(value.CustomerID);
                        $(".ContactName", row).html(value.ContactName);
                        $(".City", row).html(value.City);
                        $("[id*=dlCustomers]").append(row);
                        row = $("[id*=dlCustomers] tr:last-child").clone(true);
                        alert(row);
                    });
                },
                error: function (jqXHR, exception) {
                    alert(jqXHR.responseText);
                }
            });
            return false;
        }

<asp:DataList ID="dlCustomers" runat="server" RepeatLayout="Table" BorderStyle="Solid" Width="99%" ForeColor="#000000"
                       BackColor="#ffffff"
                       CellPadding="3"
                       GridLines="none">
                       <ItemStyle Font-Names="tahoma,arial,sans-serif"
                           Font-Size="12"
                           BackColor="#ffffff" />
                       <AlternatingItemStyle Font-Names="tahoma,arial,sans-serif"
                           Font-Size="2"
                           BackColor="#ffff00" />
                       <ItemTemplate>
                           Customer Name:
                           <asp:Label ID="ContactName" CssClass="ContactName" runat="server" Text='<%# Eval("ContactName") %>'></asp:Label><br />
                           Customer ID:
                           <asp:Label ID="CustomerID" CssClass="CustomerID" runat="server" Text='<%# Eval("CustomerID") %>'></asp:Label>
                           City:
                           <asp:Label ID="Version" runat="server" CssClass="City" Text='<%# Eval("City")%>'></asp:Label>
                       </ItemTemplate>
                   </asp:DataList>

<System.Web.Services.WebMethod(EnableSession:=True)> _
    Public Shared Function FillGridView() As Customersinfo()
        Dim dt As New DataTable()
        Dim objDll = New Clscust()
        Dim details As New List(Of Customersinfo)()
        Try
            details = objDll.GetCustInfo()
           

        Catch ex As Exception

        End Try
        Return details.ToArray()
    End Function

above code fill only two record
i'm not able to get the exact error
i'm getting 6 Records for details.ToArray() then it show Error after two records in jquery:ajax function