thank you!

there was a process:

openldap  1797  0.0  0.3  23752  4004 ?        Ssl  11:48   0:00 /usr/sbin/slapd -h ldap:/// ldapi:/// -g openldap -u openldap -f /etc/ldap/slapd.conf

after kill it i restarted without problems.
i increased the loglevel to "4" and tried another time to test the server:

ldapsearch -x -W -D 'cn=Administrator,dc=amahoro,dc=bi' -b "" -s base

with the next answer:

ldap_bind: Invalid credentials (49)

and then restarting server is failed.

checking on syslog:

Feb 22 12:06:40 debservbis slapd[1890]: connection_get(13)
Feb 22 12:06:40 debservbis slapd[1890]: ==> hdb_bind: dn: cn=Administrator,dc=amahoro,dc=bi
Feb 22 12:06:40 debservbis slapd[1890]: send_ldap_result: err=49 matched="" text=""
Feb 22 12:06:40 debservbis slapd[1890]: connection_get(13)

killed another time the openldap process. restarting is ok.

trying to change the password with ldappasswd the answer is

ldap_sasl_interactive_bind_s: Invalid credentials (49)
    additional info: SASL(-13): user not found: no secret in database

on syslog:

Feb 22 12:12:42 debservbis slapd[1958]: @(#) $OpenLDAP: slapd 2.4.23 (Jun 16 2011 02:53:39) $#012#011buildd@murphy:/build/buildd-openldap_2.4.23-7.2-i386-Y1mwvF/openldap-2.4.23/debian/build/servers/slapd
Feb 22 12:12:42 debservbis slapd[1958]: daemon: bind(8) failed errno=98 (Address already in use)
Feb 22 12:12:42 debservbis slapd[1958]: daemon: bind(8) failed errno=98 (Address already in use)
Feb 22 12:12:42 debservbis slapd[1958]: slapd stopped.
Feb 22 12:12:42 debservbis slapd[1958]: connections_destroy: nothing to destroy.

and restarting failed.

mmmmmmmmmmmm!