Generated sitemap 404 error in Google Webmaster tools

[petersen]

I'm running Joomla 2.5.4 and the content plugin 2.0.3.

The sitemap renders fine at http://www.chartercommercial.com/index.php?option=com_xmap&view=xml&id=1 but when this is submitted to Google it gives me a 404?

The only thing I can think is it might be something to do with the HTML boilerplate .htaccess file? http://html5boilerplate.com/

Any ideas?