Ajax method getting hidden field value from server side

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C#

Ajax

Through ajax call am calling GetBlinkStatus(startdate,enddate) at page load,

function getBlink(){
    var strtDate = document.newGetElementById('hidStrtDate').value;
    var endDate = document.newGetElementById('hidEndDate').value;
     Application_Home_Admin.GetBlinkStatus(strtDate, endDate , getData_callback); //Ajax call, Need to pass Schedule date from dropdownlist
    }

Server side code, changing hidden value on drop down change

if (index == 0)
            {
                fromDate = DateTime.Now.ToString(CommonSessions.CorporateDateFormat);
                toDate = DateTime.Now.ToString(CommonSessions.CorporateDateFormat);
                lblCurrentFilter.Text = GetResourceValue(ResourceFiles.DefaultLocal, "Scheduleson") + " " + GetFormattedDate(DateTime.Now);
                //GetBlinkStatus(DateTime.Now,DateTime.Now);
               <code> hidStrtDate.Value = Convert.ToString(DateTime.Now);
                hidEndDate.Value = Convert.ToString(DateTime.Now);</code>
            }
            else if (index == 1)
            {
                fromDate = currentFirstDay.ToString(CommonSessions.CorporateDateFormat);
                toDate = endDate.ToString(CommonSessions.CorporateDateFormat);
                lblCurrentFilter.Text = GetResourceValue(ResourceFiles.DefaultLocal, "Schedulesfrom") + " " + GetFormattedDate(currentFirstDay) + " " + GetResourceValue(ResourceFiles.Default, "To") + " " + GetFormattedDate(endDate);
                //GetBlinkStatus(currentFirstDay, endDate);
                <code>hidStrtDate.Value = Convert.ToString(currentFirstDay);
                hidEndDate.Value = Convert.ToString(endDate);</code>
            }

Ajax method in server side

[AjaxPro.AjaxMethod(AjaxPro.HttpSessionStateRequirement.Read)]
    public int GetBlinkStatus(string strtDate,string endDate)
    {
        int returnVal = -1;
        returnVal = Obj.GetBlinkStatusByDate(Convert.ToDateTime(strtDate), Convert.ToDateTime(endDate));
        return returnVal;
    }

Initially am passing parameters from Hidden field, so no problem in it.
But when I change hidden field value in server side, older values still persist and passed as parameter to the ajax call.

How can I overcome this issue?
Any helps will be greatly appreciated.

Regards,
RK