bdb_equality_candidates: (objectClass) index_param failed

[Mustafa Atakan <atakan@metu.edu.tr>]

hello all,

  in our university, openldap is planned to be used as an
"authentication server".  In the tests, there are some strange entries
in the log file, when there is a search. The search string is

ldapsearch -x -h localhost -b "ou=People,dc=metu,dc=edu,dc=tr"
uid=atakan

in the log:

Sep 23 11:59:20 lp3 forwarded from lp3: slapd[3063936]: conn=0 fd=10
ACCEPT
from IP=127.0.0.1:55692 (IP=0.0.0.0:389)
Sep 23 11:59:20 lp3 forwarded from lp3: slapd[3063936]: conn=0 op=0
BIND dn="" method=128
Sep 23 11:59:20 lp3 forwarded from lp3: slapd[3063936]: conn=0 op=0
RESULT tag=97 err=0 text=
Sep 23 11:59:20 lp3 forwarded from lp3: slapd[3063936]: conn=0 op=1
SRCH base="ou=People,dc=metu,dc=edu,dc=tr" scope=2
filter="(uid=atakan)"

Sep 23 11:59:20 lp3 forwarded from lp3: slapd[3063936]:
bdb(dc=metu,dc=edu,dc=tr): Locker does not exist
Sep 23 11:59:20 lp3 forwarded from lp3: slapd[3063936]: <=
bdb_equality_candidates: (objectClass) index_param failed (22)
Sep 23 11:59:20 lp3 forwarded from lp3: slapd[3063936]:
bdb(dc=metu,dc=edu,dc=tr): Locker does not exist
Sep 23 11:59:20 lp3 forwarded from lp3: slapd[3063936]: <=
bdb_equality_candidates: (uid) index_param failed (22)

Sep 23 11:59:23 lp3 forwarded from lp3: slapd[3063936]: conn=0 op=1
SEARCH RESULT tag=101 err=0 nentries=1 text=
Sep 23 11:59:23 lp3 forwarded from lp3: slapd[3063936]: conn=0 op=2
UNBIND
Sep 23 11:59:23 lp3 forwarded from lp3: slapd[3063936]: conn=0 fd=10
closed

What is the reason of:
bdb_equality_candidates: (objectClass) index_param failed (22)
bdb(dc=metu,dc=edu,dc=tr): Locker does not exist

Thank you, in advance...