Try this Code format in Code Behind
ReportViewer1.LocalReport.DataSources.Add
(new Microsoft.Reporting.WebForms.ReportDataSource("DataSet1", dt.ToList()));
ReportViewer1.LocalReport.ReportPath =
Server.MapPath("_MedicalReimburseReport.rdlc");
ReportViewer1.LocalReport.Refresh();
List<reportparameter> parameters = new List<reportparameter>();
parameters.Add(new ReportParameter("coveredDateFrom", txtFrom.Text));
parameters.Add(new ReportParameter("coveredDateTo", txtTo.Text));
parameters.Add(new ReportParameter("workSiteCode", worksiteCode));
ReportViewer1.LocalReport.SetParameters(parameters);