Crystal report problem move next page

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C#

Hello. I have a problem with move next page. Assume that i have 5 pages of report. I can only move from first page to second page only. whatever i click next button, page keep showing on second page. It doesn't move to 3rd page than 4th...

my code is below :

private ReportDocument report;
private String reportName = "ABCrpt.rpt";

protected void NextButton_Click(object sender, EventArgs e)
        {
            this.BindReport();
            this.rptviewer.ShowNextPage();
        }


private void BindReport()
        {
            if (Session["Rep"] == null)
            {
                Hashtable Params = new Hashtable();
                Params.Add("StartDate", Convert.ToDateTime(this.StartDateFlexDevCalendar.GetDate));
                Params.Add("EndDate", Convert.ToDateTime(this.EndDateFlexDevCalendar.GetDate));

                report = new ReportDocument();
                report.Load(Server.MapPath("EN/" + reportName ));


                TableLogOnInfos tblLogonInfos = new TableLogOnInfos();
                TableLogOnInfo tblLogonInfo = new TableLogOnInfo();
                ConnectionInfo connectionInfo = new ConnectionInfo();

                connectionInfo.ServerName = "sokheng";
                connectionInfo.UserID = "sa";
                connectionInfo.Password = "1234";
                connectionInfo.DatabaseName = "DatabaseABC";


                foreach (CrystalDecisions.CrystalReports.Engine.Table tbl in report.Database.Tables)
                {
                    tblLogonInfo = tbl.LogOnInfo;
                    tblLogonInfo.ConnectionInfo = connectionInfo;
                    tbl.ApplyLogOnInfo(tblLogonInfo);
                }

                if (Params != null)
                {
                    foreach (DictionaryEntry p in Params)
                    {
                        report.SetParameterValue(Convert.ToString(p.Key), Convert.ToDateTime(p.Value));
                    }
                }
                Session["Rep"] = report;
            }
            report = (ReportDocument)Session["Rep"];
            this.rptviewer.ReportSource = report;
            this.rptviewer.DataBind();
        }

So please help me ... what should I do to solve this problem ?