Blank stylesheet.xml

After installing plugin, clicked on “The URL to your sitemap index
file is: http://blog.bigsurtrailmap.net/sitemap.xml” – but it was
blank. The server log shows a successful “200” access with size 579
bytes. There _is_ a valid html file
http://blog.bigsurtrailmap.net/sitemap.html. I don’t have any SEO or
other plugins which should be generating a stylesheet. A previous post mentioned unchecking a “Use Default” box – only one I saw appeared to be for an XSLT stylesheet which I am not using – unchecked it anyhow but no change.

The page I need help with: [log in to see the link]