Thanks Moritz, your solution worked, but now I have a new Warning:
S4 Connector Rejects
Found 1 UCS rejects and 1 S4 rejects. See Univention Support Database - How to deal with s4-connector rejects for more information.
UCS DN: cn=Console Logon,cn=Builtin,dc=domainname,dc=it
S4 DN: cn=console logon,cn=builtin,DC=domainname,DC=it
S4 DN: CN=Console Logon,CN=Builtin,DC=domainname,DC=it
UCS DN: cn=console logon,cn=builtin,dc=domainname,dc=it