$sub is gecontroleerd
maar $replace is leeg
foreach ($sub as $value) {
$replace = '<ul>';
$sql = mysql_query("SELECT id,naam,url FROM '".$value."s'");
while ($objj = mysql_fetch_object($sql)) {
$replace .= '<li><a href="'.$objj->url.'">'.$objj->naam.'</a></li>';
}
$replace .= '</ul>';
$menu = str_replace($value.'s',$replace,$menu);
}