Make sure you follow these rules:
The content of the XML file should look like
this:
<div id="twitter">
<a href="https://twitter.com/share" class="twitter-share-button">Tweet</a>
<script>
<!--
!function (d, s, id) {
var
js, fjs = d.getElementsByTagName(s)[0], p = /^http:/.test(d.location) ? 'http': 'https';
if (! d.getElementById(id)) {
js = d.createElement(s);
js.id = id;
js.src = p + '://platform.twitter.com/widgets.js';
fjs.parentNode.insertBefore(js, fjs);
}
}
(document,
'script', 'twitter-wjs');
-->
</script>
</div>