google sitemap error

[ppeter]

hello!

i have an error here
http://www.vs-stainz.at/index.php?option=com_xmap&view=xml&tmpl=component&id=1

Errors
Unsupported file format
Your Sitemap does not appear to be in a supported format. Please ensure it meets our Sitemap guidelines and resubmit.

to you know why?

regards
Peter