Error: Could not change user id

Hi All

I have used PostgreSQL for SQL-Ledger in Linux (Ubuntu) for about 6months and have run into PostgreSQL
problems when it starts up.

PostgreSQL is reporting errors about changing user id so that it falls
over when the system boots.

I've read this:
http://archives.postgresql.org/pgsql-admin/2006-01/msg00273.php

I have found FAQ for Linux:
http://www.designmagick.com/article/2/Starting-Out/Installing-PostgreSQL
yet this error still occurs after changing the permissions of the postgresql directory

ie:
sudo chown -R postgres:postgres /usr/share/postgresql
sudo chown -R postgres:postgres /usr/share/postgresql-common

what happens:

Manually starting postgresql by the user postgres:
postgres@XXXX:/etc/init.d$ ./postgresql-7.4 start
chmod: changing permissions of `/var/run/postgresql': Operation not permitted
 * Starting PostgreSQL 7.4 database server:main
Error: Could not change user id                  [fail]

after changing ownership of `/var/run/postgresql' to postgres:postgres and with
permissions 4777 then the errors are less, but postgresql still doesn't
start:

postgres@XXX:/etc/init.d$ ./postgresql-7.4 start
 * Starting PostgreSQL 7.4 database server:main
Error: Could not change user id                  [fail]

I think this maybe something in /etc/postgresql/7.4/pg_hba.log  or /etc/postgresql/7.4/postgresql.conf yet I haven't
foundthe solution to get PostgreQL going. 

What could be wrong here?

How can this be fixed?

What do I need to read?

TIA

Russell