I was able to login.
The message is in the page source after saving
Code:
<article class="art-post art-messages" style="display: none;"><div class="art-postcontent clearfix"><div id="system-message-container">
<div id="system-message">
<div class="alert alert-message">
<a data-dismiss="alert" class="close">?</a>
<h4 class="alert-heading">Messaggio</h4>
<div>
<p></p><h3>Grazie asd j! Il tuo numero di registrazione ? 14CA1020 da conservare prima di stampare e da annotare sulla causale del bonifico</h3><p></p>
</div>
</div>
</div>
</div>
</div></article>
but set to display:none.
The message is shown if I disable JS in my browser.
Which may be your template.
Did you try with Protostar (and disable the other one, clear all Joomla and browser cache to get rid of old JS files...)? In post #3 you said "I'm using protostar template." but this is not the case.
One other point:
After migrating from Fabrik3.0 to 3.1/2 you must edit all your date element and set the new date format (d-m-Y instead of old %d-%m...)
http://fabrikar.com/forums/index.php?wiki/upgrading-from-3-0-to-3-1/