The google webmaster toolkit does not accept the sitemap format from the new module. It does accept formats from older modules. Maybe because there is a warning at the beginning of the file xml_google.php?

I get this warning :
Deprecated: Assigning the return value of new by reference is deprecated in /home/impresscms_be/impresscms.be/xml_google.php on line 56
Don't call this file directly

Whereas I get a XML file in the 'older' version.