title: ajax returns an error even if everything is ok
body: <p>I have this simple code</p>
  
  <p>the data is regularly saved on the server but always generates the error "Error ListaSegnalazioni! undefined"</p>
  
  <p>if I remove the instruction <code>e.preventDefault();</code> the error vanishes!</p>
  
  <p>what could be the problem?</p>
  
  <pre class="lang-js prettyprint-override"><code>    e.preventDefault();
      $.ajax({
            type: "POST",
            url: '/api/PostListaSegnalazioni/',
            data: JSON.stringify(rows),
            "dataSrc": "",
            contentType: "application/json; charset=utf-8",
            dataType: "json",
            success: function(data) {
              alert("Dati Inviati!");
            },
              error: function(xhr, status, error) {
                alert("Error ListaSegnalazioni! " + xhr.responseText);
              }
            });
  </code></pre>