He forgot a '.'
PHP Code:
$query = $vbulletin->db->query_read("SELECT * FROM " . TABLE_PREFIX . "thread ORDER BY lastpost DESC LIMIT 10");
while ($last = $vbulletin->db->fetch_array($query))
{
// If you want to link to the thread to use $lasttitle .= '<a href="showthread.php?t='. $last['threadid'] .'">'. $last['title'] .'</a><br />';
$lasttitle .= $last['title']<br />;
}