Spirou,
>> ---------------------------
>> INSERT INTO pg_group VALUES ('http_user')
>> CREATE USER "www-data" IN GROUP http_user;
>> CREATE USER nobody IN GROUP http_user;
>>
>> mybase=> select * from pg_group;
>> groname |grosysid|grolist
>> ---------+--------+-------
>> http_user| |
>> (1 row)
>>
>> mybase=> \z
>> NOTICE: get_groname: group 0 not found
>> pqReadData() -- backend closed the channel unexpectedly.
>> This probably means the backend terminated abnormally
>> before or while processing the request.
Please look at my answer for Wim Aarts question "can grolist in pg_group be
updated" in the GENERAL list. There you can found an URL for an administration
tool which handles the group access for you.
Gerald