Caldav and Carddav for MAC doesn't connect

we have a single MAC with an actual MAC-OSx that wants to connect to our Groupwise-System.
E-Mail works fine.
But connecting to caldav or carddav as described in

doesn't work.

The message I get in every variation of username or email-address, groupwise server address and with or without ssl, Gw-server or gms-server, with path or no path I've tried, is only one error message:

"Accountname/Passwort konte nicht überprüft werden"
(In englisch something like "account name / password couldn't be validated")

Is there any idea how to solve this problem?