relation "pg_user" does not exist

I am running PostgreSQL 7.4.7 on Fedora Core 3. I get a lot of
warnings from pgAdmin III:

relation "pg_user" does not exist

but it doesn't seem to prevent me from doing most operations. More
seriously, I cannot execute a backup. I get the following message:

*****************************************
/usr/bin/pg_dump -i -h localhost -p 5432 -U postgres -F c -b -v -f
"testbackupfile" rickdb
pg_dump: saving encoding
pg_dump: saving database definition
pg_dump: SQL command failed
pg_dump: Error message from server: ERROR: relation "pg_user" does
not exist
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 = 'rickdb'
pg_dump: *** aborted because of error

Process returned exit code 1.
******************************************

Indeed, if I log in as -U postgres -d template1 and select * from
pg_user, the view does not exist. Anybody have an idea why this view
was not created on install and what I can do to correct the situation?