Can't delete image

I am using metabox Version: 4.3.6.
I have an image_thickbox which uploads and displays fine, I can use the edit link but I can not delete the image from the mouse over X.
I get a javaScript alert with “undefined”.
Is there something I am doing wrong? I have tried and get the same problem with plupload and image.

Any help would be appreciated, please see code below.

function rw_BANNER_register_meta_box()
{
    // Check if plugin is activated or included in theme
    if ( !class_exists( 'RW_Meta_Box' ) )
        return;
    $prefix = 'rw_';
    $meta_box = array(
        'id'       => 'header-image',
        'title'    => 'Header Image',
        'pages'    => array( 'post', 'page' ),
        'context'  => 'normal',
        'priority' => 'high',
        'fields' => array(
            array(
                'name'  => 'Header Image',
                'desc'  => '',
                'id'    => $prefix . 'header-image',
                'type'  => 'thickbox_image',
                'clone' => false,
            ),
        )
    );
    new RW_Meta_Box( $meta_box );
}

$post_id = '';
if( isset($_POST['post_ID']) && $_POST['post_ID'] ){
    $post_id = $_POST['post_ID'];
}elseif( isset($_GET['post']) && $_GET['post'] ){
    $post_id = $_GET['post'];
}

if( $post_id ){
    $post_id =  filter_var($post_id, FILTER_VALIDATE_INT);
    if( $post_id != '2'){
        add_action( 'admin_init', 'rw_BANNER_register_meta_box' );
    }
}

http://wordpress.org/plugins/meta-box/