Have you uploaded the .htaccess file?
Basically: Google/Yahoo want the .xml/.txt file to be in the site's ROOT folder. We have to place it in the /forums/vbseo_sitemap/data/ folder for it to work.
So, we create an .htaccess that goes in the root directory, so that when we try to hit
www.rootdirectory.com/sitemap.xml, the .htaccess redirects the request to the correct location, but the Search Engine THINKS that the file is accessable at root.