So its the Report Manager URl you are getting the error on?..
(IE. http://blahblah/Reports)
Have you tried the reportServer URL (looks like a basic FTP interface (text))
(IE. http://blahblah/ReportServer)
Any errors showing is RS Configuration Manager?
You should find the Web.config for Report Manager here:
<Installation directory> \Reporting Services \ReportManager\Web.config
You may have an assembly reference to Oracle from the 2008 version that you'd need to remove. Not sure yet though. If you can post its contents *and backup before making changes*
ta