Hi @LeffDesign
In your above code, you have the AJAX call pointing to:
url: "../wp-content/themes/twentytwelve/fields/test.php",
Is this correct? If so, WP will not be loaded correctly, ACF will not be included and your PHP error will make sense.
In your first code however, you write that you are using the native wp_ajax functions.php AJAX solution.
Can you confirm which way you are coding as they dramatically will effect ACF’s usage
