Why is Output Stream not available when a custom TextWriter is used, after upgrading project to VS 2010?

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C#

objReportDocument = new ReportDocument();
objIReportDocument = ReportFactory.InitiateReportDocumentCR();
objReportDocument = (ReportDocument)objIReportDocument.GetReportDocument(objReportCallingViewData.ReportInformation.ReportFileName, vParamArrayList, objReportCallingViewData.ReportInformation.ReoprtPath, vFormulaList)

System.IO.MemoryStream vMS;
vMS = (System.IO.MemoryStream)objReportDocument.ExportToStream(ExportFormatType.PortableDocFormat);
Response.Clear();
Response.ClearContent();
Response.ClearHeaders();
Response.Buffer = true;
Response.ContentType = "application/Pdf";
Response.BinaryWrite(vMS.ToArray());
Response.Flush();
Response.End();
vMS.Dispose();

this code was working fine in visual studio 2008 but not working in visual studio 2010 and show an error message 'Output Stream not available when a custom TextWriter is used' please anybody can help me.