Problem with Javascript ad code
If you are working on Drupal 8, create a twig like html.html.twig in your themes templates folder and the put your script in there.

&lt;!DOCTYPE html&gt;
&lt;html{{ html_attributes }}&gt;
&lt;head&gt;
    &lt;head-placeholder token="{{ placeholder_token }}"&gt;
    &lt;title&gt;{{ head_title|safe_join(' | ') }}&lt;/title&gt;
    &lt;script id="mNCC" language="javascript"&gt;
    medianet_width = "600";
    medianet_height = "120";
    medianet_crid = "455208315";
    medianet_versionId = "111299";
    (function() {
    var isSSL = 'https:' == document.location.protocol;
    var mnSrc = (isSSL ? 'https:' : 'http:') + '//contextual.media.net/nmedianet.js?cid=8CUWJ3143' + (isSSL ? '&amp;https=1' : '');
    document.write('&lt;scr' + 'ipt type="text/javascript" id="mNSC" src="' + mnSrc + '"&gt;&lt;/scr' + 'ipt&gt;');})();
    &lt;/script&gt;

&lt;/head&gt;
&lt;body&gt;&lt;/body&gt;
&lt;/html&gt;