I created a report and published it to the Report Server 2008 that worked fine. I can call http://servername:81/Reports in my browser and view and expo
Check in the following folder: C:\Program Files\Microsoft SQL Server\MSRS10.OSSSQL2008\Reporting Services\ReportServer\
There are two files: -ReportService2005.asmx -ReportExecution2005.asmx
Combine these with your url above "http://servername:81/ReportServer" to form the correct link to your webservice i.e. "http://servername:81/ReportServer/ReportService2005.asmx?wsdl"