well I have had issues with vb site map since i started using it, they swear its fine. sometimes it will build fine other days you get what you describe. everyone in here has heard me rant about it. and still it has issues i guess, i say i guess because i no longer even try and use it i use a standalone site map generator and submit that. works fine and i don't drop out of google anymore since i abandoned vbs site map, good luck
i use
http://www.xml-sitemaps.com/