If you see this message, it means the web app was not properly started. For example, if you opened the index.html file directly, that would be loaded with file:// protocol in your browser. By default, modern browsers block loading local files due to CORS issues. You need to open the web app via an HTTP server.
To simplify the visualization of the web report, we provide a webreport.py script to start a HTTP server, and automatically open your browser on the starting page of the report. To simplify its use, we also provide a webreport.command (for Mac) and webreport.bat (for Windows) to easily start the Python script with a simple mouse double-click.