Hi,
I don't know what could cause the "Always use www" option not to work correctly. We'll test this issue.

Ok thank you, is important to know becouse if I try a link like villacastelbarco.com/villa-per-matrimoni and retry the same but with WWW did't redirect to right link.

I've tested both options ("Always use www domain" and "Always use non-www domain") with Joomla both in root and in a subfolder, and everything works fine, so there must be something specific to your server. Try using some developer tool (eg. Firebug in Firefox) to see what the exact redirection headers are during the infinite redirection loop.

sorry we still have the problem and need to solve. I just upgraded to 4.2.4 but no good news.
Is not possible to use any dev tool as you can see in image villacastelbarco.com/villacastelbarco-error.png
I also have a modules problem with Joomse...maybe is not compatible with Gantry Framework?
Thank you.

I've tried the URL displayed in the screenshot you posted and it seems to be working fine. Have you disabled JoomSEF or have you managed to solve the problem?
What problem do you have with modules? It is possible that there is some incompatibility with Gantry Framework, but we haven't got any reports of this yet.