Resolved by following comment on Tutsplus Tutorial (link included):
In function save_meta(), replace this line:
if (!wp_verify_nonce($_POST['custom_meta_box_nonce'], basename(__FILE__)))
with this line:
if (!isset($_POST['custom_meta_box_nonce']) || !wp_verify_nonce($_POST['custom_meta_box_nonce'], basename(__FILE__)))
See full comment here.