To solve- Warning: Parameter 1 to modMainMenuHelper::buildXML() expected to be a reference, value given in /libraries/joomla/cache/handler/callback.php on line 99
or your joomla top menu is missing
If Your currently site runs on Joomla 1.5. The previous server run PHP 5.2.9 while the new server ran a later version of PHP, 5.3.0. This error is thrown because of the reference type used in the helper file.
Locate modules/mod_mainmenu/helper.php, open the file and change the following line from