slapd why sasl error message?

To all LADAP GURU.

I installed ldap (slapd 2.4.17) on a debian machine (ARM processor). The LDAP server allows you to centralize authentication of users and unix samba (samba is set with the PDC for windows machines, all with windows 7 OS). The communication is protected by TLS / SSL. Don’t use SALS mechanism and, at the moment, I don’t want to use it. Everything works perfectly but I don’t understand why in the log file (syslog) I find the following error message:

Oct 18 14:52:10 qnapserver slapd[11916]: daemon: read active on 26

Oct 18 14:52:10 qnapserver slapd[11916]: connection_get(26)

Oct 18 14:52:10 qnapserver slapd[11916]: ==> sasl_bind: dn="" mech=DIGEST-MD5 datalen=0

Oct 18 14:52:10 qnapserver slapd[11916]: daemon: epoll: listen=8 active_threads=0 tvp=zero

Oct 18 14:52:10 qnapserver slapd[11916]: daemon: epoll: listen=9 active_threads=0 tvp=zero

Oct 18 14:52:10 qnapserver slapd[11916]: daemon: epoll: listen=10 active_threads=0 tvp=zero

Oct 18 14:52:10 qnapserver slapd[11916]: daemon: epoll: listen=11 active_threads=0 tvp=zero

Oct 18 14:52:10 qnapserver slapd[11916]: daemon: epoll: listen=12 active_threads=0 tvp=zero

Oct 18 14:52:10 qnapserver slapd[11916]: daemon: activity on 1 descriptor

Oct 18 14:52:10 qnapserver slapd[11916]: daemon: activity on:

Oct 18 14:52:10 qnapserver slapd[11916]:

Oct 18 14:52:10 qnapserver slapd[11916]: daemon: epoll: listen=8 active_threads=0 tvp=zero

Oct 18 14:52:10 qnapserver slapd[11916]: daemon: epoll: listen=9 active_threads=0 tvp=zero

Oct 18 14:52:10 qnapserver slapd[11916]: daemon: epoll: listen=10 active_threads=0 tvp=zero

Oct 18 14:52:10 qnapserver slapd[11916]: daemon: epoll: listen=11 active_threads=0 tvp=zero

Oct 18 14:52:10 qnapserver slapd[11916]: daemon: epoll: listen=12 active_threads=0 tvp=zero

Oct 18 14:52:10 qnapserver slapd[11916]: daemon: activity on 1 descriptor

Oct 18 14:52:10 qnapserver slapd[11916]: daemon: activity on:

Oct 18 14:52:10 qnapserver slapd[11916]: 26r

Oct 18 14:52:10 qnapserver slapd[11916]:

Oct 18 14:52:10 qnapserver slapd[11916]: daemon: read active on 26

Oct 18 14:52:10 qnapserver slapd[11916]: connection_get(26)

Oct 18 14:52:10 qnapserver slapd[11916]: ==> sasl_bind: dn="" mech=<continuing> datalen=265

Oct 18 14:52:10 qnapserver slapd[11916]: SASL [conn=542] Failure: realm changed: authentication aborted

Oct 18 14:52:10 qnapserver slapd[11916]: send_ldap_result: err=49 matched="" text="SASL(-13): authentication failure: realm changed: authentication aborted"

Oct 18 14:52:10 qnapserver slapd[11916]: daemon: epoll: listen=8 active_threads=0 tvp=zero

Oct 18 14:52:10 qnapserver slapd[11916]: daemon: epoll: listen=9 active_threads=0 tvp=zero

Oct 18 14:52:10 qnapserver slapd[11916]: daemon: epoll: listen=10 active_threads=0 tvp=zero

Oct 18 14:52:10 qnapserver slapd[11916]: daemon: epoll: listen=11 active_threads=0 tvp=zero

Oct 18 14:52:10 qnapserver slapd[11916]: daemon: epoll: listen=12 active_threads=0 tvp=zero

Oct 18 14:52:10 qnapserver slapd[11916]: daemon: activity on 2 descriptors

Oct 18 14:52:10 qnapserver slapd[11916]: daemon: activity on:

Oct 18 14:52:10 qnapserver slapd[11916]: 26r

This massage is displayed only after logged in from a Windows 7 client machine and is repeated approximately every 15 minutes.

Please Help me, how can I fix this?

Thanks Paolo