Shield - AD integration error

I have configured shield with Active Directory, done every thing explained by elastic but ending up with below error, what would be the cause?

cause: com.unboundid.ldap.sdk.LDAPException: An error occurred while attempting to connect to server AIPTEST-MAD.AIPTEST.LOCAL:636: Unable to verify an attempt to to establish a secure connection to 'AIPTEST-MAD.AIPTEST.LOCAL:636' because an unexpected error was encountered during validation processing: peer not authenticated