This is not so much an error/problem with EGroupware.
The problem occurs when the system tries to authenticate a user against LDAP.
If you want to approach this problem again, it makes sense to ask this in the Univention forum:
UCS is interesting if you want to run applications (which are offered in the App-Center) in a Microsoft Windows environment.
Or if you want to operate a domain on the basis of UCS as a directory service.