Warning: Parameter 1 to modMainMenuHelper::buildXML() expected to be a reference.

Error: Warning: Parameter 1 to modMainMenuHelper::buildXML() expected to be a reference.
Solution :
This error is  occurred due the php version 5.3 and joomla is not certified to work with PHP 5.3.0.
You need to change some code in your files.
open the file
vi /home/username/public/modules/mod_mainmenu/helper.php
You can change this :
Form
function buildXML(&$params)
to
function buildXML($params)