'Bad file number' error in openldap2.0.18

[Daniel Tiefnig <openldap@qmail.infonova.at>]

hi,

i'm trying to create quite a big database (730.000 mail-users) with 
slapadd of openldap2.0.18. everything seems to be ok until i try to 
search for an entry in the database. slapd -d 65535 gives me following 
error:

conn=1 op=1 SRCH base="ou=Mail-Users,o=aon,c=at" scope=2 
filter="(uid=aon.911210135.fax)"
=> ldbm_back_search
dn2entry_r: dn: "OU=MAIL-USERS,O=AON,C=AT"
=> dn2id( "OU=MAIL-USERS,O=AON,C=AT" )
=> ldbm_cache_open( "/usr/local/openldap/2.0.18/data/dn2id.dbb", 7, 600 
)
<= ldbm_cache_open NULL "/usr/local/openldap/2.0.18/data/dn2id.dbb" 
errno=9 reason="Bad file number")
<= dn2id could not open dn2id.dbb

i wasn't able to find this error-msg in openldap source, so i took a 
look at berkeley-db and in the java faq's of db3.2.9 i found an entry 
for this error relating to problems with large-file support of various 
JDK releases.. but nothing in the source.. though i can't imagine that 
this causes problems now.. :o|

however, in db-2.7.7 (what is what we're using at the moment) i wasn't 
able to find a "Bad file number" error either..

so, what i'm wondering now is 1st where does the error come from and 2nd 
what might be the cause..?
my database files are not _that_ big, i'd say:
(from `ls -l`, size in Bytes)

160653312 Dec 14 16:44 dn2id.dbb
318971904 Dec 14 16:44 id2entry.dbb
 42860544 Dec 14 16:44 mail.dbb
 32538624 Dec 14 16:44 mailAlternateAddress.dbb
     8192 Dec 14 16:44 nextid.dbb
   155648 Dec 14 16:44 objectClass.dbb
 42762240 Dec 14 16:44 uid.dbb

what i noticed, is that the files are not even about half the size of a 
(working) openldap1.2.9 server with bdb-3.2.9. that normal, or a 
possible error..?

any ideas..? (besides we should try to get openldap working with bdb-3 
or 4)

daniel