Google Webmaster Tools reports zero URLs in sitemap

XML Sitemap appears to be working correctly, and displays a sitemap when I access this link: http://www.conservationphotographers.com/sitemap.xml

However, Google Webmaster Tools reports that there are zero URLs in the sitemap, and thus Google does not bother to index the site.

Any reason why Google would think there are zero URLs in the sitemap?

Is there a way I can force XML Sitemap to produce a sitemap file so that I can manually submit it to Google?

Thank you for the help,

Keith