During my installation SSL was not active yet. I ended up with a webshop running the default content, without having access to my admin pages. No error appeared anywhere. Just returning to the admin login page, regardless of de given input there.
I remove my insallation completely (directory deleted and recreated). I ran installation again. I noticed just in time that the default "http://" was given at step 2. I changed that to "https://" and installation completed correctly including admin pages working as expected.