Check the following:
The user's login name in the Management Server must be identical to a
uidentry in the LDAP database.
Passwords should be stored in the LDAP database in either the
Plaintext passwords stored in the LDAP are not supported for security reasons.
If your LDAP is configured to only allow reading of
authPasswordfield under a certain bind name, remember to fill in the LDAP username and LDAP password fields in the administration interface.
If you require TLS authentication to the LDAP server, remember to upload a certificate in the LDAP configuration page.
If you set TLS mode to Require, make sure you have uploaded a valid certificate for TLS authentication purposes.
If the LDAP server is offline, none of the users who have been configured to be authenticated via LDAP will be able to log in.