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


This error means that the specified URL of report building server does not return 
WSDL.


In most cases it simply means that the specified URL is incorrect.


Where to find it that URL: 


WPF Viewer for Reporting Services:
reportViewer.ReportingServicesUrl = @"http://localhost/ReportServer/ReportExecution2005.asmx";


Silverlight Viewer for Reporting Services:
<MsReportingServer Url="http://localhost/ReportServer/ReportExecution2005.asmx"/>


Please check if it is set correctly. To do this, copy and paste the URL in the browser. And if the URL is correct you will see an XML document.