If you have installed a PHP application you downloaded, etc. and you get errors such as the following:
Notice: Undefined variable: VARIABLE NAME
It is most likely PHP's register globals being turned off causing the problem.
This problem can usually be attributed to a change made to PHP many versions ago that turned "register globals" off for security reasons. For more information on this, please see this web page:
To resolve this, please ask the person who wrote the PHP scripts to modify their code to work without register globals. If that is not possible, you can turn register globals back on for just your site, or just a specific directory, by placing the following text in a file named .htaccess (Note the leading period) in the directory in question:
php_flag register_globals On
Most PHP application written since 2005 should not require register globals to be enabled.