Saving images using a custom post type in wordpress?

I am trying to save some pictures to the wordpress database within a plugin I am developing (with the help of a tutorial - when I attempt to save my 'slider' post type, I am presented with the following screen:

This is the code..

add_action('save_post', 'fwds_save_slider_info');

function fwds_save_slider_info($post_id) {

    // verify nonce

    if (isset($_POST['fwds_slider_box_nonce']) && !wp_verify_nonce( $_POST['fwds_slider_box_nonce'], basename(__FILE__) )) {
       return $post_id;
    }
    // check autosave
    if (defined('DOING_AUTOSAVE') && DOING_AUTOSAVE) {
       return $post_id;
    }
    // check permissions
    if ('slidesjs_slider' == isset($_POST['post_type']) && current_user_can('edit_post', $post_id)) {

       /* Save Slider Images */

        print_r($_POST['gallery_img']);exit;

       $gallery_images = (isset($_POST['gallery_img']) ? $_POST['gallery_img'] : '');

       $gallery_images = strip_tags(json_encode($gallery_images));

       update_post_meta($post_id, "_fwds_gallery_images", $gallery_images);

    } else {
       return $post_id;
    }
}

When i go back and view the sliders I save, the images disappear; what am I doing wrong here?

via Chebli Mohamed