It looks to me like you might have the ad in the wrong table .. try changing it from this:
Old Code:
CODE
<tr valign="top" height="99%">
<td>
<img src="images/header_shadow_home.gif" width="748" height="11" alt=""><br>
<!-- BODY TABLE; BEGIN -->
<table width="748" border="0" cellpadding="0" cellspacing="0">
<script type="text/javascript"><!--
google_ad_client = "pub-6053042570648886";
google_ad_width = 728;
google_ad_height = 90;
google_ad_format = "728x90_as";
google_ad_type = "image";
google_ad_channel ="";
google_color_border = "CCCCCC";
google_color_bg = "FFFFFF";
google_color_link = "000000";
google_color_url = "666666";
google_color_text = "333333";
//--></script>
<script type="text/javascript"
src="http://pagead2.googlesyndication.com/pagead/show_ads.js">
</script>
<br>
<td>
Try this:
CODE
<tr valign="top" height="99%">
<td align="center">
<img src="images/header_shadow_home.gif" width="748" height="11" alt=""><br>
<!-- BODY TABLE; BEGIN -->
<script type="text/javascript"><!--
google_ad_client = "pub-6053042570648886";
google_ad_width = 728;
google_ad_height = 90;
google_ad_format = "728x90_as";
google_ad_type = "image";
google_ad_channel ="";
google_color_border = "CCCCCC";
google_color_bg = "FFFFFF";
google_color_link = "000000";
google_color_url = "666666";
google_color_text = "333333";
//--></script>
<script type="text/javascript"
src="http://pagead2.googlesyndication.com/pagead/show_ads.js">
</script>
<table width="748" border="0" cellpadding="0" cellspacing="0">
<td>
The main thing is that any table content must go between <td></td> tags to be valid.