[Plugin: Google XML Sitemaps] Google error: Sitemap appears to be an HTML page

Hi, i have a trouble submitting sitemap. A message says that:

“Your Sitemap appears to be an HTML page. Please use a supported sitemap format instead.”

What’s wrong with my sitemap?

http://www.sds.art.br/sitemap.xml

Thanks!!!

http://wordpress.org/extend/plugins/google-sitemap-generator/