I get this error when I run slaptest or try to start the service:

lt_dlopenext failed: (back_bdb.la) file not found
slaptest: bad configuration file!

I am running Centos 5.2.
How do I fix this?

Here is the config file.

#
# See slapd.conf(5) for details on configuration options.
# This file should NOT be world readable.
#
include /etc/openldap/schema/core.schema
include /etc/openldap/schema/cosine.schema
include /etc/openldap/schema/inetorgperson.schema
include /etc/openldap/schema/nis.schema

# Allow LDAPv2 client connections. This is NOT the default.
allow bind_v2

# Do not enable referrals until AFTER you have a working directory
# service AND an understanding of referrals.
#referral ldap://root.openldap.org

pidfile /var/run/openldap/slapd.pid
argsfile /var/run/openldap/slapd.args
#Read slapd.conf(5) for possible values
loglevel 256

# Load dynamic backend modules:
modulepath /usr/lib/openldap
moduleload back_bdb.la
# moduleload back_ldap.la
# moduleload back_ldbm.la
# moduleload back_passwd.la
# moduleload back_shell.la
#The maximum number of entries returned for a search operation
sizelimit 500
#The tool-threads parameter sets the actual amount of CPUs used for indexing
tool-threads 2

# The next three lines allow use of TLS for encrypting connections using a
# dummy test certificate which you can generate by changing to
# /etc/pki/tls/certs, running "make slapd.pem", and fixing permissions on
# slapd.pem so that the ldap user or group can read it. Your client software
# may balk at self-signed certificates, however.
# TLSCACertificateFile /etc/pki/tls/certs/ca-bundle.crt
# TLSCertificateFile /etc/pki/tls/certs/slapd.pem
# TLSCertificateKeyFile /etc/pki/tls/certs/slapd.pem

# Sample security restrictions
# Require integrity protection (prevent hijacking)
# Require 112-bit (3DES or better) encryption for updates
# Require 63-bit encryption for simple bind
# security ssf=1 update_ssf=112 simple_bind=64

# Sample access control policy:
# Root DSE: allow anyone to read it
# Subschema (sub)entry DSE: allow anyone to read it
# Other DSEs:
# Allow self write access
# Allow authenticated users read access
# Allow anonymous users to authenticate
# Directives needed to implement policy:
# access to dn.base="" by * read
# access to dn.base="cn=Subschema" by * read
# access to *
# by self write
# by users read
# by anonymous auth
#
# if no access controls are present, the default policy
# allows anyone and everyone to read anything but restricts
# updates to rootdn. (e.g., "access to * by * read")
#
# rootdn can always read and write EVERYTHING!
########################################################################
# Specific Backens directives for bdb:
# Backens specific directives apply to this backend until another
# backend directive occurs
backend bdb
checkpoint 512 30

#######################################################################
######################################################################
#Specific directives for database #1
database bdb
suffix "dc=gpinc,dc=net"
rootpw

#######################################################################
# ldbm and/or bdb database definitions
#######################################################################

database bdb
suffix "dc=my-domain,dc=com"
rootdn "cn=Manager,dc=my-domain,dc=com"
# Cleartext passwords, especially for the rootdn, should
# be avoided. See slappasswd(8) and slapd.conf(5) for details.
# Use of strong authentication encouraged.
# rootpw secret
# rootpw {crypt}ijFYNcSNctBYg

# The database directory MUST exist prior to running slapd AND
# should only be accessible by the slapd and slap tools.
# Mode 700 recommended.
directory /var/lib/ldap

# Indices to maintain for this database
index objectClass eq,pres
index ou,cn,mail,surname,givenname eq,pres,sub
index uidNumber,gidNumber,loginShell eq,pres
index uid,memberUid eq,pres,sub
index nisMapName,nisMapEntry eq,pres,sub
#Save the time that the entry gets modified, for database #1
lastmod on

#admin can read write all passwords
#users can change their own passwords
access to attrs=userPassword,ShawdowLastChange
by dn="cn=admin,dc=gpinc,dc=net" write
by anonymous auth
by self write
by * none
#many applications need read access to the rootDSE
#especially to read supported SASL mechnisms
#this restricts them to the rootDSE; they cannot read past this level
access to dn.base="" by * read

# admin gets unlimited read/write access to database
# everyone else read-only
access to *
by dn="cn=admin,dc=gpinc,dc=net" write
by *read





# Replicas of this database
#replogfile /var/lib/ldap/openldap-master-replog
#replica host=ldap-1.example.com:389 starttls=critical
# bindmethod=sasl saslmech=GSSAPI
# authcId=host/ldap-master.example.com@EXAMPLE.COM

Most likely openldap was not configured with dynamic module support, so comment out the lines
an see if it works.