It was brought to our attention that in some installations using IIS 7 a managed handler must be added for the report viewer web control, otherwise a 404 - File or Directory not found message is displayed when viewing sql reporting services reports.  This issue was confirmed by a customer and corrected by taking this additional step in IIS to register the handler in addition to the web.config handler modifications.

1. Open the IIS by typing the "inetmgr" in run command.
2. Goto your site in the list of web sites and select it.
3. Now, see the Features view area. Here, you can see all options available for the web site. From all the options select "Handler Mappings".
4.  Now, click on the "Handler Mappings" section then you will see all the mappings applied for that web site. Now, on the right side panel, you are able to see all the options available for the handler mappings. Select the option "Add Managed Handler"
5. When you click that link, you will see a popup window with the text boxes.
Request Path = Reserved.ReportViewerWebControl.axd,
Type = Microsoft.Reporting.WebForms.HttpHandler, Microsoft.ReportViewer.WebForms, Version=9.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
Name= Reserved.ReportViewerWebControl.axd
6. Click OK and do IISRESET.

If anyone has any questions or issues with this, please post here.