For this to work, you will also need the directory "google-sitemaps" in the server root, which must be writable by the Web server.The generated sitemaps can be downloaded at [ad_url]/google-sitemaps/index.xml. See
http://www.clasohm.com/google-sitemaps/index.xml
according to the
Sitemaps docs, a sitemap can only refer to pages below it in the site hierarchy - so a map at
http://example.com/google-sitemaps/index.xml will only be used for other pages below
http://example.com/google-sitemaps/. So for this to actually help it looks like the sitemap file needs to be placed directly in the site root directory.