wpmu-dev-seo can't generate sitemap.xml

The XML page cannot be displayed
Cannot view XML input using XSL style sheet. Please correct the error and then click the Refresh button, or try again later.

--------------------------------------------------------------------------------

The stylesheet does not contain a document element. The stylesheet may be empty, or it may not be a well-formed XML documen...

this is the error we have when we try to access the xml
site url: http://rc-fever.com.au/

additional to that we find it will go to a blank page if we try to save setting.