In your GroupWise Admin Console --> System --> LDAP Servers --> the configuration of your AD Directory --> the Address that you filled in, is it an IP address or a DNS name? Also, what did you set the Base DN to on the same screen?
When you manually associate the user are you doing it on the user object itself, or are you going to System --> Directory Associations --> and doing a search for the user? When you configured the MMC plugin did you enter the IP address (same as your LDAP settings in GW Admin Console) or did you perhaps use a DNS name?
I would test the following in the GroupWise Admin Console --> System --> Directory Associations --> your Base DN should display as "ou=kabe,dc=kabe,dc=ch". Leave context empty and select Search Sub-Tree. See if that is able to search for users that need to be associated.