Crystal Report: Missing Parameter Values

Question

Hi! I am new to Crystal report, application is in ASP.net 3.5 and MySQL 5.1, going to develop report between dates like from date and to date, first page of report is shown good but when i tried to navigate on another page i got error like Missing Parameter Values same error i got in Printing and Export action Thanks in advance

public partial class BookingStatement : System.Web.UI.Page {

//DAL is my Data Access Layer Class

//Book is ReportClass

DAL obj = new DAL();
Book bkStmt = new Book();
protected void Page_Load(object sender, EventArgs e)
{

    if (!IsPostBack)
    {
       //crvBooking is Crystal Report Viewer
       //reportFill method is to fill Report 

        reportFill();
        crvBooking.EnableViewState = true;
        crvBooking.EnableParameterPrompt = false;
    }


   /* Also try reportFill() out side !IsPostBack but didn't work */


    //Check if the parmeters have been shown.
 /*   if ((ViewState["ParametersShown"] != null) && (ViewState["ParametersShown"].ToString() == "True"))
    {
        bkStmt.SetParameterValue(0, "20/04/2010");
        bkStmt.SetParameterValue(1, "20/04/2010");
    }*/

}


protected void crvBooking_navigate(object sender, CrystalDecisions.Web.NavigateEventArgs e)
{
   // reportFill();
}

protected void reportFill()
{

    //bkStmt.rpt is Report file
    //bookingstatment is View
    //bkStmt is ReportClass object of Book

    string rptPath = "bkStmt.rpt";

    string query = "select * from bookingstatment";


    crvBooking.RefreshReport();
    crvBooking.Height = 600;
    crvBooking.Width = 900;



    bkStmt.ResourceName = rptPath;


    String dtFrm = bkStmt.ParameterFields[0].CurrentValues.ToString();

    obj.SetCommandType(CommandType.Text);
    obj.CommText = query;
    DataTable dtst = obj.GetDataTable();

    crvBooking.ParameterFieldInfo.Clear();



    ParameterDiscreteValue discretevalue = new ParameterDiscreteValue();
    discretevalue.Value = "20/04/2010"; // Assign parameter
    ParameterValues values = new ParameterValues();
    values.Add(discretevalue);

    bkStmt.SetDataSource(dtst);

    ViewState["ParametersShown"] = "True";
    crvBooking.EnableViewState = true;

    bkStmt.DataDefinition.ParameterFields[0].ApplyCurrentValues(values);
    bkStmt.DataDefinition.ParameterFields[1].ApplyCurrentValues(values);


    crvBooking.ReportSource = bkStmt;
}

}