Try This:
Code:
<script type=\"text/javascript\"><!--
google_ad_client = \"pub-9937811682735223\";
/* 120x240, created 4/4/09 */
google_ad_slot = \"1398716991\";
google_ad_width = 120;
google_ad_height = 240;
//-->
</script>
<script type=\"text/javascript\"
src=\"http://pagead2.googlesyndication.com/pagead/show_ads.js\">
</script>
Sometimes the PHP doesn't like quotes so escaping them with backslashes \ should help. :)