Multiple Post Thumbnails plugin and attachment error

You should trigger the function on some other hook like

function add_multiple_post_thumbnails_from_plugin() {  
  new MultiPostThumbnails( array(  
         'label'     => 'Thumbnail Image' 
        ,'id'        => 'video-thumbnail'
        ,'post_type' => 'video'  
  ) );  
}  
add_action( 'admin_init', 'add_multiple_post_thumbnails_from_plugin' );