password authentication failed for user postgres

Hi,

1. I have added  listen_addresses = '*' ; in  postgresql.conf

2. And have made the following changes to pg_hba.conf

local   DATABASE    USER   METHOD
local    samegroup      all      password
host    DATABASE    USER    CIDR-ADDRESS  METHOD  [OPTION]
host          all                 all       0.0.0.0/0             md5
hostssl      all                 all       0.0.0.0/0            md5

3. Have restarted the server

4. I can login to the server as user postgres.

But  while trying to createuser I get the following message  :
'createuser: could not connect to database postgres:  FATAL :
password authentication failed for user "postgres"

This is on Redhat running Plesk also.

I am new to Linux as well as PostgreSQL. Help would be much appreciated.

Thanks
Viv