Thanks for this valuable suggestion : I tried with Thunderbird, no XML data and the log is more explicit :
Server returned timed out [help]
Sorry, an error occurred while trying to validate this feed. Possible causes:
-The address may be incorrect. Make sure the address is spelled correctly. Try loading the feed directly
in your browser to make sure a feed exists at that address.
-The feed may be temporarily unavailable. The server may be down, or too slow. Try again later.
-The validator may be busted. If the feed exists, the server is fine, and the problem is reproducible,
let us know on the feedvalidator-users mailing list.
The [help] says :
Your feed couldn't be validated because there was a problem downloading it from the web server. You should try to diagnose this using a web browser, and make sure that the URL you supplied resolves to an accessible file. This usually means that the URL was wrong, or that permissions on the server don't allow us to fetch that file. The error shows the message that the server sent, which may help.
-> I guess there is some restriction either in my apache2.conf, or in my Mediawiki folder. I just need to know where.
Thanks, E