problems with pg_dump

Hi!

I have a debian woody with postgresql 7.4.2. When i try to use pg_dump i
get the next error:

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 = 'db' 
pg_dump: *** aborted because of error

I want to do a daily backup, otherway to do this without pg_dump?

Thanks,

    Suela.