I had some problems with encoding the links of my utf-8 web site. I have change the "setCharSet" of the functions.inc.php from "iso-8859-1" to "utf-8" file and everything seems to work now.
Oups ! It's not enough. I have also done (but be careful, this is just a fast and non secure modification to match my site):
I added the line :
$url = utf8_decode($url);
just before this line (around 165) :
$data = array('url' => $url);
in the file inc/gsgxml/GsgXml.class.php
But again, be careful, these corrections have been made after a
very quick analysis of the code to let me get the right sitemap.