This seems to be a bug in the extension, try using this code instead:
<div id="custom-tweet-button"> <a href="http://twitter.com/share?url=<?php echo urlencode('http://new.primaveralife.com.mx/contenidos/detalle.php?pr=' . $row_rsDetalle['pr_id'] . '&mn=' . $row_rsDetalle['cont_men_id'] . '&sc=' . $row_rsDetalle['cont_secc_id'] . '&ct=' . $row_rsDetalle['cont_id']); ?>" target="_blank" title="Tweet"></a> </div>
please post back with your result.
thanks.