Hello Malte,
are you using oracle?
strange, the no available pools is something that I haven't found yet in our prod/dev servers....
where did you get the ns_ldap module?
here's our config.tcl nsldap section:
#
# ldap pool ldap
#
ns_section "ns/ldap/pool/ldap"
ns_param user "cn=Manager, o=Your University"
ns_param password "yourpass"
ns_param host "ldap.server.edu"
ns_param connections 1
ns_param verbose On
#
# ldap pools
#
ns_section "ns/ldap/pools"
ns_param ldap ldap
#
# ldap default pool
#
ns_section "ns/server/${server}/ldap"
ns_param Pools *
ns_param DefaultPool ldap
are you trying direct call to ns_ldap or through acs-authentication authority?