I tested out the Animals example with Baobab, and it always throw an exception on the following code? What did I do wrong? thanks.

public function appendChild($id_parent=NULL,$fields_values=NULL){
$id_parent=intval($id_parent);
if (!$this->db->multi_query(”
CALL Baobab_{$this->forest_name}_AppendChild({$this->tree_id},{$id_parent},@new_id,@cur_tree_id);
SELECT @new_id as new_id,@cur_tree_id as tree_id”)) {
throw new sp_MySQL_Error($this->db);
}