squid 3

I already configured squid.conf as follow

auth_param basic program /usr/lib/squid/squid_ldap_auth -b "dc=bnhproj,dc=com" -f "uid=%s" -h tbwoffice1.bnhproj.com
auth_param basic children 5
auth_param basic realm Squid proxy-caching web server
auth_param basic credentialsttl 2 hours

when i enter this command output like this
# /usr/lib/squid/squid_ldap_auth -b "dc=bnhpro,dc=com" -f "uid=%s" -h tbwoffice.bnhpro.com
vhargude 12345
squid_ldap_auth: ../../../libraries/libldap/search.c:189: ldap_search: Assertion `ld != ((void *)0)' failed.
Aborted

i am using rhel4 32 bit and squid 3

How i resolv this problem.