"Notice: Undefined index: und in include()" Since this morning, I get this message on my website.

It says the error is on line 7 in my template file, but when I look at the line 7 the code on it is &lt;?php if (!$page): ?&gt;.

My template file looks like the following.

&lt;div id="node-&lt;?php print $node-&gt;nid; ?&gt;" class="&lt;?php print $classes; ?&gt;"&gt;
  &lt;div class="node-inner"&gt;
    &lt;?php if (!$page): ?&gt;
      &lt;h2&lt;?php print $title_attributes; ?&gt;&gt;      
      &lt;?php if (($type == "article") &amp;&amp; ($node-&gt;field_add_taxonomy_tag_articles[$node-&gt;language][0]['tid'] == 26)): ?&gt;
        &lt;a href="/discoveries#node-&lt;?php print $node-&gt;nid; ?&gt;"&gt;&lt;?php print $title; ?&gt;&lt;/a&gt;&lt;/h2&gt;
      &lt;?php else:?&gt;
        &lt;a href="&lt;?php print $node_url; ?&gt;"&gt;&lt;?php print $title; ?&gt;&lt;/a&gt;&lt;/h2&gt;
      &lt;?php endif; ?&gt;
    &lt;?php endif; ?&gt;
    &lt;?php print $user_picture; ?&gt;
    &lt;?php if ($display_submitted): ?&gt;
      &lt;span class="submitted"&gt;&lt;?php print $date; ?&gt; Ñ &lt;?php print $name; ?&gt;&lt;/span&gt;
    &lt;?php endif; ?&gt;
    &lt;div class="content"&gt;
      &lt;?php
        hide($content['comments']);
        hide($content['links']);
        print render($content);
      ?&gt;
      &lt;?php if (!empty($content['links'])): ?&gt;      
        &lt;span class="links"&gt;
          &lt;?php print render($content['links']); ?&gt;
        &lt;/span&gt;
      &lt;?php endif; ?&gt;
    &lt;/div&gt;      
    &lt;?php if (!empty($content['links']['terms'])): ?&gt;
      &lt;div class="terms"&gt;
        &lt;?php print render($content['links']['terms']); ?&gt;
      &lt;/div&gt;
    &lt;?php endif;?&gt;  
  &lt;/div&gt; &lt;!-- /node-inner --&gt;
&lt;/div&gt; &lt;!-- /node--&gt;
&lt;?php print render($content['comments']); ?&gt;'
The line that is causing that error message is the following one.

&lt;?php if (($type == "article") &amp;&amp; ($node-&gt;field_add_taxonomy_tag_articles[$node-&gt;language][0]['tid'] == 26)): ?&gt;


'und' is the value for the constant LANGUAGE_NONE, which is used for $node-&gt;language, when the node is language-neutral.  

When you want to obtain the value of a field, you should use field_get_items(), as in the following code.

&lt;?php $items = field_get_items('node', $node, 'field_add_taxonomy_tag_articles'); ?&gt;
&lt;?php if (($type == "article") &amp;&amp; ($items[0]['tid'] == 26)): ?&gt;