I'm running PHP 4.4.9 (not by my choice), so this probably doesn't apply to anyone using a language that hasn't been discontinued for 4 years, but if it does affect you it's a quick fix. Steps follow.
wordpress/wp-content/plugins/simple-page-ordering/simple-page-ordering.phpin your editor of choice.
- At line 54, change this...
add_filter( 'views_' . get_current_screen()->id, array( $this, 'sort_by_order_link' ) );
$current_screen = get_current_screen(); add_filter( 'views_' . $current_screen->id, array( $this, 'sort_by_order_link' ) );
- Save/refresh and the error is gone!