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:
- Open IIS 7 or 7.5
- Select the site to modify by double clicking, revealing all options.
- Double click on Handler Mappings
- Click Add Managed Handler
- Request path: Reserved.ReportViewerWebControl.axd
- Type: Microsoft.Reporting.WebForms.HttpHandler
- Name: Reserved-ReportViewerWebControl-axd
- Click OK to complete
Refresh the application or web page using the Report Viewer, it should work properly now.