รบกวนช่วยแก้ให้หน่อยคับ Fatal error: Call to a member function Children() on a non-object in

// Get document
		$xml = JFactory::getXMLParser('Simple');
		$xml->loadString($xmls[$type]);
		$doc = &$xml->document;

		$menu	= &JSite::getMenu();
		$active	= $menu->getActive();
		$start	= $params->get('startLevel');
		$end	= $params->get('endLevel');
		$child	= $params->get('showAllChildren');
		$path	= array();

		// Get subtree
		if ($start)
		{
			$found = false;
			$root = true;
			if(!isset($active)){
				$doc = false;
			}
			else{
				$path = $active->tree;
				for ($i=0,$n=count($path);$i<$n;$i++)
				{
					foreach ($doc->children() as $child) 
					{
						if ($child->attributes('id') == $path[$i]) {
							$doc = &$child->ul[0];
							$root = false;
							break;
						}
					}
	
					if ($i == $start-1) {
						$found = true;
						break;
					}
				}
				if ((!is_a($doc, 'JSimpleXMLElement')) || (!$found) || ($root)) {
					$doc = false;
				}
			}
		}