So I've found the source of your XML parsing errors. Something is inserting invalid and non-printing UTF-8 characters into your site's posts.
Validating your feed now shows an invalid token at line 290, column 406, which is this tag ...
<a href="http://www.alessiorinelli.it" target="_blank" title=" Alessio Rinelli On The Web " class="wp-biographia-link-">Web</a>
... if you look closely, the title attribute has what looks like some extra spaces ... I've replaced them here with underscores so you can see what I mean ...
title="_Alessio Rinelli_ On _The Web_"
But as they're not printing characters, you can't easily spot them. So I downloaded your feed into a text file and looked at the contents in a text editor which shows all characters, not just the printable ones and I see this ...
title="^BAlessio Rinelli^D On ^BThe Web^D"
... there are these extra -- and invalid -- characters in every link's title attribute. This isn't just in the code that WP Biographia emits, but it's in the content of every one of your site's posts as well.
I suspect that there's another plugin you have running which is hooked to the WordPress the_content filter that is doing this and that it's running before WP Biographia and so my plugin picks up this invalid content as well.
I strongly suggest that you disable all of your plugins, validate your feed and if it validates successfully (which I suspect it will) then start to re-enable them, one by one, checking your feed each time, until you identify which plugin it is which is causing this.
It could also be something inherent in your theme, so I'd recommend reverting temporarily to a stock WordPress supplied theme, such as TwentyTen, to rule this out.
-Gary