Error in sitemap

Hi there!
I've installed the Sitemaps and Seo plugin in my WP network

The instructions sais it'll automatically generate a sitemap for each blog,
but I get an error and you can see it

What should I do to solve this?
could I get the sitemap of the entire wp network, with all the blogs, to submit in google webmaster tools?
it's this a wise move?

P.S. I've WPMU DEV SEO installed too