When deploying an app using SSRS to a new server, sometimes the Report Viewer Control does not like to work without a tweak or two. I sometimes get a 404 on the report viewer control. The parameters will show up and the header controls, but not the body of the report. The body of the report has a 404 error in it. If you user Fiddler to check out a little closer you'll see the 404 error originates from the reportviewer control itself

404 http http://test.url.net/Reserved.ReportViewerWebControl.axd?OpType=Resource&Version=9.0.21022.227&Name=Microsoft.Reporting.WebForms.Icons.ChevronUp.gif

Well, here's the Fix.

1. Open IIS Manager
2. Click on the server in the tree on left
3. In the options click on Handler Mappings
4. Under Actions click on Add Managed Handler
5. Fill out the following values
6. 1.Request path: Reserved.ReportViewerWebControl.axd
7. 2.Type: Microsoft.Reporting.WebForms.HttpHandler, Microsoft.ReportViewer.WebForms, Version=9.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
8. 3.Name: Reserved-ReportViewerWebControl-axd
9. Click OK
10. BOOM - works on my machine...