I have installed a trial version on my server to generate sitemap, and then I used the generated sitemap.xml to run the validation test at http://www.xml-sitemaps.com/validate-xml-sitemap.html
The sitemap.xml did not pass validation and the error seemed to result from unicode characters in urls.
Here is my sitemap: [external links are visible to admins only]
I see there's an UTF8 charset checkbox but I don't know if I should check it or not.
I use some other character set like "BIG5".