I switched over to your sitemap after using Yoast's WordPress SEO. Google Webmaster Tools began putting the big red 'X' on those sitemaps with the warning:
Sitemap is HTML
Your Sitemap appears to be an HTML page. Please use a supported sitemap format instead.
Now they've begun doing it for yours too. I'm hoping that someone else has known how to resolve this one. The sitemap comes up find when I bring it up
and there's definitely no HTML coding i it, so I'm a little stumped.
I don't know if W3 Total Cache is creating a little issue with this or now.