You have WPML
It has very old, outdated sitemap code.
They will fix it couple of months :(
But it is OK for robots! Only the XML stylesheet is buggy.
see: http://validator.w3.org/
bugreport:
http://wpml.org/forums/topic/please-update-wpseo_xml_sitemaps_filter/
If you need a visually correct sitemap mail me: viktor@szepe.net