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Notice: Undefined index: depth in book_made_simple_link() (line 515

Can you test this :
in book_made_simple.module, replace :

function book_made_simple_link($type, $node = null, $teaser = false) {
  $links = array();

by

function book_made_simple_link($type, $node = null, $teaser = false) {
  $links = array();
  if (isset($node->in_preview)) return $links;

Folder: sites/all/modules/book_made_simple/

Link: https://www.drupal.org/node/1810806