ASP.Net Error: Cannot find a control with ID CrystalReportSource1, referenced by CrystalReportViewer1.ReportSourceID

Error :

Cannot find a control with ID 'CrystalReportSource1', referenced by CrystalReportViewer1.ReportSourceID.

<CR:CrystalReportViewer ID="CrystalReportViewer1" runat="server" AutoDataBind="True"
    Height="1123px" ReportSourceID="CrystalReportSource1" ViewStateMode="Inherit"
    Width="763px" ToolPanelView="None" />

report.Load(Server.MapPath("Reports/Purchase_Order2.rpt"));
report.SetDatabaseLogon(ch.UserID, ch.password, ch.ser, ch.database);
report.SetParameterValue("@Purchase_order_no", Session["Purchase_order_no"].ToString());
report.SetParameterValue("@Company", Session["Company_sht_code"].ToString());
report.SetParameterValue("@user", Session["User_Id1"].ToString());
CrystalReportViewer1.ReportSource = report;
CrystalReportViewer1.Font.Size = 15;

Thank you