Hi Cyril Wasem,
The custom errors settings in the web.config are related to the requests handled by the ASP.NET. Therefore it works fine for pages with .aspx extensions.
In the case when using extensionless request to http://exchange.pixit.com:8000/JLMD/fr/home
, the 404 error is thrown by the IIS, because it does not reach to the ASP.NET.
In order to allow extensionless requests to be handled by the ASP.NET application, you should set wildcard mapping in the IIS, or use the sf404.aspx approach described in the User Manual -> Extensionless URLs topic.
the Telerik team