I have modified pdf_thumbnails_admin_int to add a new hook on updated_post_meta and works fine:
function pdf_thumbnails_admin_int()
{
if (!extension_loaded(‘imagick’)) {
add_action(‘admin_notices’, ‘pdf_thumbnails_missing_imagick’);
return;
}
add_filter(‘wp_generate_attachment_metadata’, ‘pdf_thumbnails_generate_attachment_metadata’, 10, 2);
add_action(‘deleted_post’, ‘pdf_thumbnails_deleted_post’);
add_action(‘updated_post_meta’, ‘pdf_thumbnails_generate_attachment_metadata’,10,2);
}
I think this error hapen becouse wordpress 3.9 use now mysqli driver, then the function the plugin must use is mysqli_real_escape_string or use wordpress function like $wpdb->prepare.
