I've double checked all the settings and everything seems fine. The xml sitemap is not generated, but the html page is created. The site is a Zen cart site. There is one other strange problem; a broken link is show for [external links are visible to admins only]. If I exclude this url, i don't get the error. (the site has a 301 redirect to exclude www and point everything to [external links are visible to admins only].)
Any help appreciated.