This is most likely to be caused by continuation references generated by the LDAP server for LDAP referrals to other parts of the directory. Referrals are often stored using the host name of the target LDAP server, which, in the case of a self-referral, can be the name of the original host to which the connection was made. If it is not necessary to follow the continuation references, this can be disabled from the Configuration Wizard. Select the 'Data Source', 'LDAP' page and click the 'Advanced' button. Change 'Continuation references' to ignore.
On Active directory servers, it may be possible to avoid continuation references by connecting to port 3268 on the server rather than port 389. If it is necessary to follow the continuation references, the problem must be resolved either in the LDAP server or on the Client host.
For Unknown Host errors, the problem is most likely to be a failed DNS lookup. Ensuring DNS is working correctly on the computer from which Schemus is run should resolve the issue. Alternatively, the hostnames and IP addresses of the referred servers could be added to the hosts file.
For Connection Refused errors, the problem is likely to be due to incorrect referral information or a failure in the LDAP service on the referred server. Ensure that all the referred LDAP servers are running and/or update the referral entries on the LDAP server.