[Plugin: WordPress SEO by Yoast] Robots.txt warning

Hi there,
I decided to use yoast’s sitemap functionality after having used Google XML Sitemaps for quite a while.
I have disabled this plugin and deleted the sitemap.xml from both my server and webmaster tools.

After submitting my news sitemap http://www.mrmad.net/sitemap_index.xml
a receive the following warning that robot.txt is preventing some urls from being indexed.
The problem is, those urls that show up as and example are not part of the sitemap, they belong to other domain which currently not active at all.

http://www.mrmad.de/wp-content/uploads/CATHARSIS-SAMSARA-CD-1-295×300.jpg

If I change .de to .net I can access those images
How can I get rid of these warnings?

http://ww.wp.xz.cn/extend/plugins/wordpress-seo/