Crystal Reports Parameters Values are not getting refresh

Hello Readers. I have developed a web based inventory and accounts system application using Sql Server 2008, Asp.net using c#.net. I have used crystal reports for reporting. Everything on reporting side is working fine. Yesterday i came across , that my parameters on the report were not getting refreshed which were initially working absolutely fine.

I give you are scenario and will present the code to analyise e.g i am running a report that contains ParamDate1 and ParaDate2 parameters in crystal reports which i want to use to show on the report. The values are getting pass to these parameters using controls and code for this is

    ReportDocument RptDoc;
    ParameterFieldDefinition PFD;
    ParameterValues PV;
    ParameterDiscreteValue PDV;

private void SetDate1AndDate2Parameters(ReportDocument RptDoc)
    {
        //Date 1 Parameters
        PV = new ParameterValues();
        PDV = new ParameterDiscreteValue();

        PFD = RptDoc.DataDefinition.ParameterFields["ParamDate1"];
        PDV.Value = Convert.ToDateTime(Date1TextBox.Text);
        PV.Add(PDV);
        PFD.ApplyCurrentValues(PV);

        //Date 2
        PV = new ParameterValues();
        PDV = new ParameterDiscreteValue();

        PFD = RptDoc.DataDefinition.ParameterFields["ParamDate2"];
        PDV.Value = Convert.ToDateTime(Date2TextBox.Text);
        PV.Add(PDV);
        PFD.ApplyCurrentValues(PV);
    }

Now the code that runs the report  is under the following

switch(ReportTitleHiddenField.Value)
{
 case "CostOfGoodsSold":
                ReportPath = "~/Reports/CostOfGoodsSold.rpt";
                DataSet CostOfGoodsSoldDS = FillCostOfGoodsSold();
                RptDoc = new ReportDocument();
                RptDoc.Load(Server.MapPath(ReportPath));
                RptDoc.SetDataSource(CostOfGoodsSoldDS);
                RptDoc.Subreports[0].SetDataSource(FillHeadersReportInfo());
                SetDate1AndDate2Parameters(RptDoc);
                //SetCurrencyAndRateParameters(RptDoc);
                //SetMethodParameter(RptDoc);
                CrystalReportViewer1.ReportSource = RptDoc;                
                CreateLog(RptDoc.SummaryInfo.ReportTitle,
               "From Date : " + Date1TextBox.Text.Trim() + " To Date : " + Date2TextBox.Text.Trim() +                
               " Currency : " + CurrencyDDL.SelectedValue + " Rate : " + GetCurrentCurrencyRate());
                break;
}

The report run aboslutely fine with this code. now problem here is when i run this for the first time. parameters do get values what i select and show them on the report perfectly but they are not show the subsequent times instead it shows the same old values that were selected on the first run.

I do know the alternative for this  to use i.e.

ParameterFields PFs = new ParameterFields();
        ParameterField PFDate1 = new ParameterField();
        ParameterDiscreteValue PDVDate1 = new ParameterDiscreteValue();
        PFDate1.Name = "ParamDate1";        
        PDVDate1.Value = Convert.ToDateTime(Date1TextBox.Text.Trim());
        PFDate1.CurrentValues.Add(PDVDate1);
        PFs.Add(PFDate1);

        ParameterField PFDate2 = new ParameterField();
        ParameterDiscreteValue PDVDate2 = new ParameterDiscreteValue();
        PFDate2.Name = "ParamDate2";
        PDVDate2.Value = Convert.ToDateTime(Date2TextBox.Text.Trim());
        PFDate2.CurrentValues.Add(PDVDate2);
        PFs.Add(PFDate2);

        CrystalReportViewer1.ParameterFieldInfo = PFs;

But I want to know that what is wrong with my code that was working fine before. plus. when using this above mentioned approach i have to handle some crystal report viewer event to give parameters their values as my report page do post back on ChangeParameterOption, Refresh,Export which i am doing manually in the code.

I am waiting for you guidance in this. Thanks in advance.