If this is related IIS 7.5 Detailed Error – 404.3  – Not Found

We need to map json or CSS like blow

1- Open your project’s Web.config file
2- Under <system.webServer> add the MIME mapping to handle the file extension you need, like so:

3- Rebuild the solution and watch for the same error. Most likely this should resolve the issue handling .less files. You can add handlers for any type of file with another <mimeMap fileExtension=” mimeType=”” />