Report viewer Error message "client found response content type of '' but expected 'text xml' The request failed with an empty response."

I'm getting the error

client found response content type of '' but expected 'text xml' The request failed with an empty response.

when I try to execute the following code.

//create a PDF from the SQL report
ReportViewer rview = new ReportViewer();

rview.ServerReport.ReportServerUrl = new Uri("http://server/ReportServer$MSSQL2K5?");

List<ReportParameter> paramList = new List<ReportParameter>();
paramList.Add(new Microsoft.Reporting.WinForms.ReportParameter("Batch", "1"));
paramList.Add(new Microsoft.Reporting.WinForms.ReportParameter("InvoiceNo", "0"));
rview.ServerReport.ReportPath = "Report/Report Invoice";

rview.ServerReport.SetParameters(paramList);

string mimeType, encoding, extension, deviceInfo;
string[] streamids;
Microsoft.Reporting.WinForms.Warning[] warnings;
string format = "PDF"; //Desired format goes here (PDF, Excel, or Image)             

deviceInfo =
"<DeviceInfo>" +
"<SimplePageHeaders>True</SimplePageHeaders>" +
"</DeviceInfo>";

byte[] bytes = rview.LocalReport.Render(format, deviceInfo, out mimeType, out encoding, out extension, out streamids, out warnings);

The error occurs on the line:

rview.ServerReport.SetParameters(paramList);

The address is correct as I can load the report fine via a web browser:

this.webBrowser1.Navigate("http://server/ReportServer$MSSQL2K5?/Report/Report Invoice&Batch=1&InvoiceNo=0");

I need to load the report with the report viewer so I can export as PDF.