Just replaced all the files with the older version and guess what? It works! I get a sitemap with seperate files for each language.
Thanks Mike!!! :)
Nevertheless and perhaps I should be really gratefull ... ;) I do regret that I have to use this plugin instead of the simple Google XML Sitemap plugin I always use together with the equally simple SEO of the Genesis Framework.
But for now I'm happy. Hope it works for you too Picks44!