Just installed the appliance in ESXi5.5 environment. Unable to join AD domain as it says there is authentication failure. After selecting to finish to try correcting the problem, unable to login to managment console as root. It says authentication failure for that also. Attempts to login to the CLI on the VM console as root fails also stating "login incorrect". I have deleted the device and reinstalled numerous times with the same results.
Have you already looked at the documentation for the appliance at https://doc.owncloud.org/server/latest/admin_manual/enterprise/appliance/index.html?
This might be a known issue with the univention system, when joining a domain.
Can you reach out to univention directly please, help in the forum is very responsive and excelent.
You can also try the updated version, using univention 4.2, which was released this week.