网上找的例子是这样的

  private void button2_Click(object sender, EventArgs e)
         {
 
             FastReport.TfrxReportClass report = new FastReport.TfrxReportClass();
             report.MainWindowHandle = (int)this.Handle;
             report.LoadReportFromFile("report\\jhjl.fr3");//添加报表路径
 
 	    FrxDataTable rptdataset1 = new FrxDataTable("adoquery1");
             FrxDataTable rptdataset2 = new FrxDataTable("adoquery2");
 
             OleDbDataAdapter oleDbDataAdapter1 = new OleDbDataAdapter("select * from TZ_Unit", Class1.conn1);
             oleDbDataAdapter1.Fill(rptdataset1);
             OleDbDataAdapter oleDbDataAdapter2 = new OleDbDataAdapter(listsql, Class1.conn1);
             oleDbDataAdapter2.Fill(rptdataset2);
 
            // rptdataset1.AssignToReport(true, report);
            // rptdataset2.AssignToReport(true, report);
            // rptdataset2.AssignToDataBand("MasterData1", report);
 
             report.ShowReport();
         }
 

我照着这个用第二次打开报表报错，后来发现.ClearDatasets();方法，要在实例后添加，第二次不报错。

report = new TfrxReportClass();
                 report.ClearDatasets();
                 report.SetGlobalVariable("Language", "Chinese");