pg_hba.conf and groups

I am trying to allow individuals within a PostgreSQL (v7.4) group to
connect to the backend.  The relevant line in pg_hba.conf is (I
believe):

    host    <db>    +<group>    <IP address>/32    md5

Note that I have replaced the contents of the real fields with <...>,
but that these match across what follows.  I understand the + to allow
access to members of the group.

The contents of the system catalogs include the following:

     # select * from pg_catalog.pg_shadow;
    usename   | usesysid | usecreatedb | usesuper | usecatupd | passwd | valuntil | useconfig
     -------------+----------+-------------+----------+-----------+--------+----------+-----------
      <name>      |      105 | f           | f        | f         | md5... |          |

     # select * from pg_catalog.pg_group;
      groname | grosysid |        grolist
     ---------+----------+-----------------------
      <group> |      100 | {100,101,102,104,105}

Nevertheless, the following command fails:

     psql --host <dbhost> --dbname=<db> --username=<name>
     psql: FATAL:  no pg_hba.conf entry for host "<IP address>", user "<name>", database "<db>", SSL off

Have I set this up incorrectly?  Is there any way to query the backend
in order to identify who it thinks has access to what?

Thanks for your help.

Cheers,
Brook