In window app and web base app, it is the same.
Let try:
string Server = "http://hn-sd-0100-wk/ReportServer_SQL2008R2";
string reportProject = "/ReportProjectContact/";
string reportName = "ReportContact";
reportViewer1.ProcessingMode = ProcessingMode.Remote;
ServerReport serverReport;
serverReport = reportViewer1.ServerReport;
serverReport.ReportServerUrl = new Uri(Server);
serverReport.ReportPath = reportProject + reportName;
ReportParameter[] rp = new ReportParameter[1];
rp[0] = new ReportParameter("OrderID", txtOrderID.Text);
reportViewer1.ServerReport.SetParameters(rp);
reportViewer1.RefreshReport();