I have a link structure http://7horses.eu/wp/blog/image/image_name/ and I understood this is a problem (syxtra's href link to images doesn't work)  but I don't know how to change it without breaking my site. Any hints what I can do ?  I deactivated syxtra for now.

SOLVED for now

I've changed in symbiostock-xtra.php

define('PLR_WP_HOME_URL', home_url() ); // instead of  get_site_url()
to
define('PLR_WP_HOME_URL', 'http://7horses.eu/wp/blog/');

just have to remember this when upgrading.