Getting error Warning: Parameter 1 to modMainMenuHelper::buildXML() expected to be a reference, value given in /libraries/joomla/cache/handler/callback.php on line 99
This error happens because the version of Joomla! you are running is not compatible with PHP 5.3.0 . You could get this error for the reason being that your host upgraded to PHP 5.3.0
A quick solution will be is to open the file modules/mod_mainmenu/helper.php in your root folder and change the following line from
function buildXML(&$params)
to
function buildXML($params)
at the top of helper.php
The best solution will be to upgrade your Joomla! installation to the latest Joomla! release