[otrs] Installation issue, can not login

Hello everyone, I got a problem with the installation of otrs-5.0.13. It should run on a ubuntu 16.04 server with apache as a webserver and MariaDB as database. I followed the installation procedure on https://otrs.github.io/doc/manual/admin/stable/en/html/manual-installation-o... until step 9. Unfortunately I'm not able login with the password provided in step 8. Has anyone encountered that problem before? If not, has someone an idea what causes the problem? If asked I will provide additional information about my system. Kind Regards, David