The error occurs because the SQL Server Reporting Services(SSRS) server is configured to accept connections only via HTTPS.
Update the RSReportServer.config file using the following steps:
1.       In Windows Explorer, locate the ReportServer directory. The following path is the default path of this directory: C:\Program Files\Microsoft SQL Server\MSRS10.MSSQLSERVER\Reporting Services\ReportServer
2.       Right-click RSReportServer.config, click Open With, click Notepad and then click OK.
3.       Locate the following Add Key entry: <Add Key="SecureConnectionLevel" Value="2"/>
4.       Change the Value setting from 2 to 0.

 
 
See also http://support.microsoft.com/kb/2011889

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