First of all i had installed version 5.0.2 running, i now installed 5.1. This didn't solve the problem. I found out that WebUI was not starting because of the value wrapper.java.maxmemory=1024 in the file jetty-service. I reduced this to 768 and managed to start WebUI. But i think that is where it also fails by the installation, WebUI had to be started before apache can start and i believe at that moment apache is also configured. I copied an apache.conf from another installation and replaced it on my server. After that i also managed to start apache and could login into the On-Command Unified Manager.