Hi there,
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"
"Windows10" {97ee9907-ab0d-43fa-bdb5-99b18aa6da32}
"Ubuntu19.04" {119829dd-4e85-4c97-9fca-b9fc4647c734}
Unfortunately I don't know how to fix this.