How to add item to $vars[breadcrumb] in Drupal
I hope that you have set $breadcrumb in page.tpl.php.
Secondly, you do not need to do it by using theme_preprocess_page. 

Just implement using THEME_breadcrumb like this:

function theme_breadcrumb($variables) {
  $breadcrumb = $variables['breadcrumb'];
  $output = '';
  if ((arg(0) == 'node') &amp;&amp; is_numeric(arg(1)) &amp;&amp; ($node = node_load(arg(1)))) {
    if ($node-&gt;type == 'TYPE NAME') {
      $breadcrumb[] = $node-&gt;title;
    }
  }
  if (!empty($breadcrumb)) {
    $output.= '&lt;div class="breadcrumb"&gt;' . implode(' › ', $breadcrumb) . '&lt;/div&gt;';
  }
  return $output;
}