水晶报表主从表问题

我用的dataset.xsd作为数据源
报销设计用到主从表 出库和出库明细 浏览时候报
登录失败。详细资料： crdb_adoplus : 未将对象引用设置到对象的实例。文件 C:\DOCUME~1\wang\LOCALS~1\Temp\UplowReport {518B3CFD-9F92-490A-8950-3E2B6FAF111E}.rpt 但是我把字表数据源和报表字段全部删掉 只留主表就没问题 我后台代码如下string uplowid = "55";            string sql = string.Format(@"SELECT SerialID, BillId, DepotClass, CreateTime,CheckTime,TotalNum, TotalWeight, Memo, CreatePerson, CheckPerson, State, YSerialID, Flag FROM tblUpLow where serialid={0};", uplowid);
             string sql1= string.Format(@"SELECT tblUPLowDetail.DetailID, tblUPLowDetail.MainID, tblUPLowDetail.ProductID, 
      tblUPLowDetail.LocationID, tblUPLowDetail.Num, tblUPLowDetail.Level, 
      tblUPLowDetail.Batch, tblUPLowDetail.Weight, tblUPLowDetail.LocationCode, 
      tblUPLowDetail.DepotID, tblDLocation.LocationName, tblDepot.DepotName, 
      tblProduct.ProductCode, tblProduct.ProductName
FROM tblUPLowDetail INNER JOIN
      tblProduct ON tblUPLowDetail.ProductID = tblProduct.ProductId INNER JOIN
      tblDepot ON tblUPLowDetail.DepotID = tblDepot.DepotID INNER JOIN
      tblDLocation ON tblUPLowDetail.LocationID = tblDLocation.LocationID where mainid={0};", uplowid);                   DataTable dt = ACO.DBUtility.DbHelperSQL.ExecuteDataTable(sql, "tblUpLow");
           DataTable dt1 = ACO.DBUtility.DbHelperSQL.ExecuteDataTable(sql1, "tblUpLowDetail");
            CrystalReportSource1.ReportDocument.Load(Server.MapPath("~/cryreport/UplowReport.rpt"));
            CrystalReportSource1.ReportDocument.SetDataSource(dt);
            CrystalReportSource1.ReportDocument.SetDataSource(dt1);
            CrystalReportSource1.DataBind();
            CrystalReportViewer1.ReportSource = CrystalReportSource1;
            CrystalReportViewer1.DataBind();
请问是怎么回事