我的Crystal报告出了什么问题？运行时，它显示缺少参数值

Question

我的Crystal报告出了什么问题？运行时，表示缺少参数值，

            CrystalDecisions.CrystalReports.Engine.ReportDocument reportDocument = new CrystalDecisions.CrystalReports.Engine.ReportDocument();
            ParameterField paramField = new ParameterField();
            ParameterFields paramFields = new ParameterFields();
            paramField.Name = "@ID";
            ParameterDiscreteValue paramDiscreteValue = new ParameterDiscreteValue();
            paramDiscreteValue.Value = patient_ID;
            paramField.CurrentValues.Add(paramDiscreteValue);
            paramFields.Add(paramField);

            paramField = new ParameterField();
            paramField.Name = "@Med";
            paramDiscreteValue = new ParameterDiscreteValue();
            paramDiscreteValue.Value = Request.QueryString["param1"];
            paramField.CurrentValues.Add(paramDiscreteValue);
            paramFields.Add(paramField);

            paramField = new ParameterField();
            paramField.Name = "@Year";
            paramDiscreteValue = new ParameterDiscreteValue();
            paramDiscreteValue.Value = Request.QueryString["param2"];
            paramField.CurrentValues.Add(paramDiscreteValue);
            paramFields.Add(paramField);

最后，

            reportDocument.Load(Server.MapPath("CrystalReport1.rpt"));
            CrystalReportViewer1.ReportSource = reportDocument;
            CrystalReportViewer1.ParameterFieldInfo = paramFields;

我在这里缺少什么？