I discovered I made a mistake... I used the following script on the website
<?php
ob_start();
page_content(1);
$content1=ob_get_contents();
ob_end_clean();
ob_start();
page_content(2);
$content2=ob_get_contents();
ob_end_clean();
if ($content2=="") { ?>
<div id="twitter_div-1">
TWITTER
</div>
<?php } else { ?>
<div id="twitter_div-2">
TWITTER
</div>
<?php } ?>
And this caused the error

, so now the sitemap module works again! There's only one thing... the droplets don't work anymore on the page on which I use the sitemap module... any help ?