Simply Static stopped working / wrong URLs

Simply Static stopped working for me. With every run it rewrites the URL in the links and just adds the last parts of the URL (after the point). So, first, a link looks like:

http://url.de

next
http://url.de.de

and so on. It throws error messages like these:

https://capture.dropbox.com/rB0U61DDVP9pJGMl

this effects also the links to the stylesheets, so the generated site is broken.