SEF not working.. is this .htaccess problem.

Hi..

I have searched the forums and tried a variety of configurations in the .htaccess file, but each time I switch on SEF url's, I get this message..

The requested URL /content/section/1/2/ was not found on this server.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

I don't have any third party SEO's installed as far as I know..

Here is the basic content of my .htaccess file..
(I have stripped out commented lines just for this posting)

##
# @version $Id: htaccess.txt 4756 2006-08-25 16:07:11Z stingrey $
# @package Joomla
# @copyright Copyright (C) 2005 Open Source Matters. All rights reserved.
# @license http://www.gnu.org/copyleft/gpl.html GNU/GPL
# Joomla! is Free Software
##

Options FollowSymLinks

RewriteEngine On

RewriteBase /

RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} ^(/component/option,com) [NC,OR] ##optional - see notes##
RewriteCond %{REQUEST_URI} (/|\.htm|\.php|\.html|/[^.]*)$ [NC]
RewriteRule ^(content/|component/) index.php

RewriteCond %{QUERY_STRING} mosConfig_[a-zA-Z_]{1,21}(=|\%3D) [OR]
RewriteCond %{QUERY_STRING} base64_encode.*$.*$ [OR]
RewriteCond %{QUERY_STRING} (\<|%3C).*script.*(\>|%3E) [NC,OR]
RewriteCond %{QUERY_STRING} GLOBALS(=|\[|\%[0-9A-Z]{0,2}) [OR]
RewriteCond %{QUERY_STRING} _REQUEST(=|\[|\%[0-9A-Z]{0,2})
RewriteRule ^(.*)$ index.php [F,L]

php_value session.save_path "/vhost/vhost6/p/e/n/penaltyactiongroup.co.uk/tmp"

ErrorDocument 404 /error/404page.html

The hosting company told me to insert that last line, as any invalid link was going to one of their default pages...

Does anyone have any ideas on where I am going wrong?