Francesco,
Sure, we can help. The main time we've heard of this is with Gavick templates, as their templates strip out Facebook buttons. If you're using a Gavick template, I'd recommend you contact them to see how you can stop their template from stripping out the Facebook code.
If you're not using a Gavick template, can you post (or Private Message) the URL of your site, and we can take a look at the front-end to see if there's anything we see that could be causing the problem.
Thanks,
Alex