Ubuntu Server 12.04: StartTLS

[admus]

Hello,
I'm following 
https://help.ubuntu.com/12.04/serverguide/openldap-server.html#openldap-tls-replication
 how to:
LDAP serwer starts correctly but when I tries to test StartTLS:
ldapsearch -x -H ldap:/// -ZZ -d -1
I gets the following error:
TLS: peer cert untrusted or revoked (0x42)
TLS: can't connect: (unknown error code).
ldap_err2string
ldap_start_tls: Connect error (-11)
    additional info: (unknown error code)
Any idea?