接続文字列を Configuration.AppSettings 内に配置しました。
CrystalReportSource CrystalReportSource1 = new CrystalReportSource();
CrystalReportViewer CrystalReportViewer1 = new CrystalReportViewer();
CrystalReportViewer1.ReportSource = CrystalReportSource1;
CrystalReportViewer1.EnableParameterPrompt = false;
CrystalReportSource1.Report.FileName = "Report3.rpt";
CrystalReportSource1.EnableCaching = false;
CrystalReportSource1.ReportDocument.SetParameterValue(0, ponumber);
CrystalReportSource1.ReportDocument.SetParameterValue(1, receiptno);
TableLogOnInfo logOnInfo = new TableLogOnInfo();
logOnInfo.ConnectionInfo.ServerName = ConfigurationManager.AppSettings["WarehouseReportServerName"];
logOnInfo.ConnectionInfo.DatabaseName = ConfigurationManager.AppSettings["WarehouseReportDatabaseName"];
logOnInfo.ConnectionInfo.UserID = ConfigurationManager.AppSettings["WarehouseReportUserID"];
logOnInfo.ConnectionInfo.Password = ConfigurationManager.AppSettings["WarehouseReportPassword"];
TableLogOnInfos infos = new TableLogOnInfos();
infos.Add(logOnInfo);
CrystalReportViewer1.LogOnInfo = infos;
maindiv.Controls.Add(CrystalReportSource1);
maindiv.Controls.Add(CrystalReportViewer1);
CrystalReportViewer1.DataBind();