I found an old thread where someone faced a similar issue but unfortunately all mentioned steps did no solve my problem. As of I log in into OMV webinterface I get "VirtualBox error: rc=0x80070005 The object functionality is limited (0x80070005)".
As of I run vboxmanage list vms no machines will be displayed. Same command as root is displaying two machines:
su vbox -c "vboxmanage list vms"
Unfortunately I don't know how to fix this.