Caused by: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
Your client truststore doesn't trust the LDAP server's certificate. You need to either get it signed by a CA or else export it from the server into all the client truststores. It is ultimately easier and cheaper to get it signed.
