When utilizing ASP.NET Report Viewer you may receive a 404 File or directory not found error. This is because the managed handler is missing in IIS for the domain serving your .NET application.

To resolve this issue:

  1. Open IIS 7 or 7.5
  2. Select the site to modify by double clicking, revealing all options.
  3. Double click on Handler Mappings
  4. Click Add Managed Handler
  5. Request path: Reserved.ReportViewerWebControl.axd
  6. Type: Microsoft.Reporting.WebForms.HttpHandler
  7. Name: Reserved-ReportViewerWebControl-axd
  8. Click OK to complete

Refresh the application or web page using the Report Viewer, it should work properly now.