Data in custom meta box not saved

I had it working, but now it’s not working any more.

I’ve added some custom metaboxes to my edit post page and I have the following problems:

1. Meta data not stored (was working)
2. Medta not deleted when empty (was not working wen 1. was working).

Is there something wrong with my code?

I got the following code in my functions.php file:

add_action( 'admin_menu', 'create_custom_meta_box' );
add_action( 'save_post', 'save_custom_post_meta_box', 10, 2 );

function create_custom_meta_box() {
  add_meta_box( 'Intro', __('Intro'), 'post_intro_meta_box', 'post', 'normal', 'high' );
}

function save_custom_post_meta_box( $post_id, $post ) {

  if ( !current_user_can( 'edit_post', $post_id ) )
		return $post_id; 

  // Custom intro text box (Ingress)
  // If custom field does not exists, it is created.
  // Then add, update and delete handles are added
  /*--------------------------------------------------------------------------- */  

  if ( !wp_verify_nonce( $_POST['post_intro_meta_box_nonce'], plugin_basename( __FILE__ ) ) )
		return $post_id;
  // Mini intro
  $meta_value = get_post_meta( $post_id, '_post_mini_intro', true );
  $new_meta_value = stripslashes( $_POST['post_mini_intro'] );

  if ( $new_meta_value && '' == $meta_value )
	add_post_meta( $post_id, '_post_mini_intro', $new_meta_value, true );

  elseif ( $new_meta_value != $meta_value )
	update_post_meta( $post_id, '_post_mini_intro', $new_meta_value );

  elseif ( '' == $new_meta_value && $meta_value )
	delete_post_meta( $post_id, '_post_mini_intro', $meta_value );
}