The firetank advanced sitemap is not an XML sitemap it sounds as if you are trying to send it to the google XML sitemap services. The advanced sitemap is and HTML sitemap it's purpose is for search engine spider linkage via a visible public sitemap as opposed to the XML sitemap you're probably trying to submit it to.
We have an XML feed which will accomplish the google XML data sitemap stuff as part of our feed manager series take a look at the x-cart feed category on
http://www.firetanksoftware.com for more information on data feeds.