Oracle Message TNS-12168 - TNS: Unable to contact LDAP Directory Server

ERRORTNS: Unable to contact LDAP Directory Server
CAUSECannot contact LDAP directory server to get Oracle Net configuration.
ACTIONVerify that the directory server is up and accessible from the network. Verify that directory access configuration is correct. For more information see the Oracle Internet Directory Administrators Guide or the Oracle Net Administrators Guide.