crystal report showing error

Protected void gv_PurchaseOrderView_RowDeleting(object sender, GridViewDeleteEventArgs e)
{
    lblPoId.Text = (string)gv_PurchaseOrderView.DataKeys[e.RowIndex].Value;
    lblPoType.Text = "PODUMMY";
   bill();
  //  billcry();

}

public void billcry()
{

    ReportDocument cryRpt = new ReportDocument();
    cryRpt.Load(Server.MapPath("CrystalReport1.rpt"));

    conn.Open();
    cmd = new SqlCommand("SELECT company_name.tinno from company where                                                 purchase_id='" + lblPoId.Text.Trim() + "'", conn);
    ad = new SqlDataAdapter(cmd);
    dt=new DataTable();
    ad.Fill(dt);
    conn.Close();



    cryRpt.SetDataSource(dt);
    CrystalReportViewer1.ReportSource = cryRpt;

}