ERROR: did not find '}' at end of input node (again)

This happend again, but now, postgresql tells me where it happens:

pg_dump: SQL command failed
pg_dump: Error message from server: ERROR: did not find '}' at end of
input node
pg_dump: The command was: select (select usename from pg_user where
usesysid = datdba) as dba, pg_encoding_to_char(encoding) as encoding,
datpath from pg_database where datname = 'dc'
pg_dumpall: pg_dump failed on database "dc", exiting

template1=# select usename from pg_user;
ERROR: did not find '}' at end of input node

\d pg_user
********* QUERY **********
SELECT c.oid,
n.nspname,
c.relname
FROM pg_catalog.pg_class c
LEFT JOIN pg_catalog.pg_namespace n ON n.oid = c.relnamespace
WHERE pg_catalog.pg_table_is_visible(c.oid)
AND c.relname ~ '^pg_user$'
ORDER BY 2, 3;
**************************

********* QUERY **********
SELECT relhasindex, relkind, relchecks, reltriggers, relhasrules
FROM pg_catalog.pg_class WHERE oid = '16683'
**************************

********* QUERY **********
SELECT a.attname,
pg_catalog.format_type(a.atttypid, a.atttypmod),
(SELECT substring(d.adsrc for 128) FROM pg_catalog.pg_attrdef d
WHERE d.adrelid = a.attrelid AND d.adnum = a.attnum AND a.atthasdef),
a.attnotnull, a.attnum
FROM pg_catalog.pg_attribute a
WHERE a.attrelid = '16683' AND a.attnum > 0 AND NOT a.attisdropped
ORDER BY a.attnum
**************************

********* QUERY **********
SELECT pg_catalog.pg_get_viewdef('16683'::pg_catalog.oid, true)
**************************

ERROR: did not find '}' at end of input node

I think (hope) I can save the data by copying the data on another computer
and start postgresql there and then dump it (just like I did last time).

The problem is, why does this happen and how can I prevent it ? Maybe this
is caused by an unproper shutdown of postgresql ?

SELECT VERSION();
version
------------------------------------------------------------------------------------------------------------------
PostgreSQL 7.4 on i686-pc-linux-gnu, compiled by GCC gcc (GCC) 3.3.2 20031022 (Gentoo Linux 3.3.2-r2, propolice)