Jade,
This was in fact due to a bug that has been fixed for the next minor release of SmarterStats 9, due out later this week, on 9/4/2014.
The cause was an XML Mime type that was not getting correctly identified as XML.
We have tested the fix against the site you mentioned and it does correctly find the sitemap file as it should.
Grady Werner
SmarterTools Inc.
www.smartertools.com