index_param failed on ipHostNumber

[Robert Fitzpatrick <lists@webtent.net>]

I setup a new lookup in our Postfix just like the one we have used for
transports for some time, but now using ipHostNumber to allow relay.
After setting up, I started receiving...

Mar  7 09:43:04 esmtp slapd[22766]: <= bdb_equality_candidates: (ipHostNumber) index_param failed (18)

So, I added ipHostNumber to my list of indexes already established for
other Postfix lookups...

# Following indexes for postfix virtual lookups
index   associatedDomain,mail,mailLocalAddress,ipHostNumber          eq

The errors go away, but now my lookup does returns nothing. And as soon
as I remove the index and try lookup again, it returns the result fine,
but slow of course and with the error above. However, even with it
removed, I still see the index in my file system...

esmtp# ls -lah /home/openldap/ipHostNumber.bdb 
-rw-------  1 ldap  ldap   8.0K Mar  7 08:32 /home/openldap/ipHostNumber.bdb

Can someone offer some guidance on what I should try next?

Thanks in advance.

-- 
Robert