Login / logout – cannot find server

Suddenly – I get this problem when I login/logut:

URL is: https://www.discosuperfly.biz/travel/wp-login.php

and page is “cannot find server”
The page cannot be displayed
The page you are looking for is currently unavailable. The Web site might be experiencing technical difficulties, or you may need to adjust your browser settings.

+++etc…

… temporarily I solve this by just manually editing the URL to point to the admin/dashboard…, but this is annoying and if this is not a known problem/bug – I guess I have to reinstall the whole system.