SetParameterValue didn't work in Button1_Click

Tonyzhoulc

public string ConString = System.Configuration.ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {

            this.WebReport_DFMMonthlyReport.Prepare();
        }
        

    }
    protected void WebReport_DFMMonthlyReport_StartReport(object sender, EventArgs e)
    {
        Report Freport3 = (sender as WebReport).Report;

        Freport3.Load(Server.MapPath(@"Bin\Report\report.frx"));
        Freport3.Dictionary.Connections[0].ConnectionString = ConString;
        Freport3.SetParameterValue("@from", "2014-01-01");
        Freport3.SetParameterValue("@to", "2014-01-31");
       // Freport3.Prepare();
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        var Freport2 = WebReport_DFMMonthlyReport.Report;
       
        FastReport.Export.ExportBase exp = new FastReport.Export.ExportBase();
        Freport2.Load(Server.MapPath(@"Bin\Report\report.frx"));
        Freport2.Dictionary.Connections[0].ConnectionString = ConString;
        Freport2.SetParameterValue("@from", TextBox_DFXFinishDate.Text);
        Freport2.SetParameterValue("@to", TextBox_FOTime.Text);
        Freport2.Prepare();
      

    }

When the click of a button, display is not the correct information. SetParameterValue didn't work.
why?