User manager LDAP import Active Directory is empty


after setting the LDAP settings in the User Manager, ths status says connected however import fails.
I want to start the search on the base dn.

In the console fwconsole userman sync --verbose I get:

ldap_search(): Search: Operations error

When adding CN=Users in front of the base DN, I get only the users in that folder, looks like its not searching deeper in the tree.
please help