Crystal Report Windows Forms Viewer The parameter is incorrect after running the crystal report

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C#5.0

CrystalReports

I have created one simple report with a sub report.
When i run it there is no any error while debuging but after it gives error "The parameter is incorrect ".

i have not created any parameter in main as well as sub report.
i am using two dataset here is code.

ds = ReportsClass_obj.Select_Employee_Report();
ds2 = ReportsClass_obj.Select_Student_DMW()
rptRatioReportNew RatioReport = new rptRatioReportNew();
                            RatioReport.Subreports[0].DataSourceConnections.Clear();

RatioReport.SetDataSource(ds.Tables[0]);

RatioReport.Subreports[0].SetDataSource(ds2.Tables[0]);
rptViewer.ReportSource = RatioReport;
rptViewer.Refresh();
rptViewer.Show();

Please help me out...!