cannot pass report parameter values and always display parameter prompt window

I created a crystal report which pass two date parameters.
formula is

{GetNoOfDays.PlugOnDate} >= {?StartDate} and {GetNoOfDays.Date} <= {?EndDate}

and I think I passed parameters correctly. but when I select two dates from datepickers and press load button, the default parameter prompt window is shown. I cant find which one is wrong.

code as below...

public partial class WindowReport1 : Window
    {

        ParameterFields paraFields = new ParameterFields();
        ParameterField paraField1 = new ParameterField();
        ParameterDiscreteValue paraDescritValue1;
        ParameterField paraField2 = new ParameterField();
        ParameterDiscreteValue paraDescritValue2;

        public WindowReport1()
        {
            InitializeComponent();
            crystalReportsViewer1.Owner = this;
        }

        private void btnLoad_Click(object sender, RoutedEventArgs e)
        {                          
                    paraField1.Name = "StartDate";
                    paraField1.CurrentValues.Clear();
                    paraDescritValue1 = new ParameterDiscreteValue();
                    paraDescritValue1.Value = datePicker1.SelectedDate;
                    paraField1.CurrentValues.Add(paraDescritValue1);
                    paraFields.Add(paraField1);

                    paraField2.Name = "EndDate";
                    paraField2.CurrentValues.Clear();
                    paraDescritValue2 = new ParameterDiscreteValue();
                    paraDescritValue2.Value = datePicker2.SelectedDate;
                    paraField2.CurrentValues.Add(paraDescritValue1);
                    paraFields.Add(paraField1);

            crystalReportsViewer1.ViewerCore.ParameterFieldInfo = paraFields; 
 
            ReportDocument report = new ReportDocument();
            report.Load("../../CrystalReport1.rpt");
          
            using (comocoLTSDataContext dc = new comocoLTSDataContext())
            {
                report.SetDataSource(from c in dc.VNoOfDays
                                     select new { c.VesselRef, c.ContainerNo,                                           c.PlugOnDate, c.PlugOnTime, c.Date, c.Time, });
            }
            
            crystalReportsViewer1.ViewerCore.ReportSource = report;
            //crystalReportsViewer1.ViewerCore.RefreshReport();
 
        }}}

can anyone give quick solution as it is urgent, please.....

[Edit]Code block added[/Edit]

Tags: C#, WPF, LINQ, CrystalReports