Q:

String was not recognized as a valid DateTime - but it runs smoothly in another server

My current Win 2008 R2 server migrating to Azure. So that Im moving a web application to Azure Server Win 2008 R2.
Currently, I am facing the issue where it shows

"Message":"String was not recognized as a valid DateTime.","StackTrace":"   at System.DateTimeParse.Parse(String s, DateTimeFormatInfo dtfi, DateTimeStyles styles)\r\n   at System.Convert.ToDateTime(String value)\r\n   at... `

Purpose of the code: Its a JQGrid library, If the code runs successfully, I will proceed to update a table. This code runs when user clicks the update button and before updating the table as validation of date.
Weird question is: My On-Prem server runs this code smoothly, all data in Azure and On-Prem server are same.
NEWLY ADDED: When I edit some rows (so far only 1 row out of 100), it works.
Working row details: 
Not working row details: 
JQuery code snippet: 
        closeAfterEdit: true,
        closeOnEscape: true,
        reloadAfterSubmit: true,
        url: '/SFI/WebService/StaffMaster.asmx/CheckEditStaff_AssignedRoster',
        ajaxEditOptions: { contentType: 'application/json; charset=utf-8' },
        mtype: 'post',
        datatype: 'json',
        serializeEditData: function (postData) {
            var PrivilegeID = $('#hdnMAPrivilegeID').val();
            eStaffID = $("#StaffID").val();
            eStaffNo = $("#StaffNo").val(),
            eNewEndDate = $("#EffectiveEnd").val();
            eStaffName = $("#StaffName").val(),
            eIdentificationNo = $("#IdentificationNo").val(),
            eDOB = $("#DOB").val(),
            eEffectiveStart = $("#EffectiveStart").val(),
            eEffectiveEnd = $("#EffectiveEnd").val(),
            eGradeCode = $("#GradeDetails").val(),
            eStaffType = $("#StaffType").val(),
            eOrgUnit = $("#OrgUnit").val(),
            eEmail= $("#Email").val().toLowerCase()

            return JSON.stringify(
            {
                StaffID: $("#StaffID").val(),
                NewEndDate: $("#EffectiveEnd").val(),
                OldEndDate: StaffOldEndDte
            });
            .
            .
            .
            StaffOldEndDte = $("#EffectiveEnd").val();

Web Service Call in C#: 
    public string CheckEditStaff_AssignedRoster(string StaffID,string NewEndDate,string OldEndDate)
    {
        string status = "0";
        bool Changed = false;
        DateTime dtnew;
        DateTime dtOld;

        dtnew = Convert.ToDateTime(NewEndDate);
        dtOld = Convert.ToDateTime(OldEndDate);

        if ((dtOld != dtnew)  && (dtnew < dtOld))
        {                
            Changed = true;
        }
        else
        {
            status = "1";
        }

        if (Changed)
        {                
            if (some condition...)
            {
                .
                .
                //do something...
            }
            else
            {
                status = "1";
            }
        }

        return status;
    }

A:

After knowing some knowledge on different cultures on DateTime format, from the question's comment, I moved to search again on how to make it the same as my on-premise server to new azure server (Because I have already developed a working code in my on-premise server). Found that, i can just change the 'Region and Language' setting same as on-premise to azure. Below is the link I used.
Here is the link: From where CultureInfo.CurrentCulture reads culture

