you may also try these codes:
paste it on functions.php
add_action('wp_head', 'load_scripts'); // to load jquery on the font page
add_action('admin_head', 'load_scripts'); // to load jquery on the admin page
function load_scripts(){
wp_enqueue_script('jquery');
}
From http://webdev-tuts.com/wordpress/jquery-is-not-defined-in-wordpress-3-4.html
here’s another fix. Add these codes on your plugin.
add_action(‘wp_head’, ‘load_scripts’);
add_action(‘admin_head’, ‘load_scripts’);
function load_scripts(){
wp_enqueue_script(‘jquery’);
…
}
From http://webdev-tuts.com/wordpress/jquery-is-not-defined-in-wordpress-3-4.html
