The reportviewer timeout expired error is normally along the lines of Unhandled exception occurred: System.Web.HttpException (0x80004005): Request timed out. It looks like reporting services is timing out however running the report within SSRS itself is fine, the error only occurs when it is run within an asp application.
The easiest fix I have found for this is to add this key to the web.config for the asp application that is calling reportviewer.aspx
Either edit or add within the
<system.web> <httpRuntime executionTimeout="7200" /> </system.web>
Dont get sidetracked by trying to update the reporting services config files, because this is purely to do with IIS and the web.config setting.