Advert Has Disappeared

Hello, My adverts have been working perfectly for months until today. My Sky Scrapper Advert on the left hand side has disappeared on the main page.

http://www.smokincharliebrown.com

On Firefox there’s just a blank, but on IE8 I get this message.

“The webpage cannot be found
HTTP 400

Most likely causes:
There might be a typing error in the address.
If you clicked on a link, it may be out of date.

What you can try:
Go back to the previous page.

More information
This error (HTTP 400 Bad Request) means that Internet Explorer was able to connect to the web server, but the webpage could not be found because of a problem with the address.
For more information about HTTP errors, see Help”

The strange thing is is that the advert appears fine on individual posts and other pages, it’s just the main page it doesn’t show up on.

Here’s the Ad Code below that I’ve been using

<script type=”text/javascript”><!–
google_ad_client = “ca-pub-XXXXXXXXXXXXXXXX”;
/* 120×600, created 18/11/10 */
google_ad_slot = “XXXXXXXXXX”;
google_ad_width = 120;
google_ad_height = 600;
//–>
</script>
<script type=”text/javascript”
src=”http://pagead2.googlesyndication.com/pagead/show_ads.js”&gt;
</script>

Anyone have any ideas?

Thanks