error when trying to enable clean urls : The requested URL /admin/settings/clean-urls was not found on this server.

As the title suggests, I am getting this error when trying to enable clean urls:

"The requested URL /admin/settings/clean-urls was not found on this server."

I have seen some other posts about this which suggest some edits to the .htaccess file, but so far copy and pasting and making small edits etc to the file has not worked. I know it will be long but I will put my .htaccess file on the bottom of the post. I'm not sure if it matters but the url the site is currently on is www.alextestsite.mediafxgroup.com, and it is NOT in a sub-directory.

Any and all help would be greatly appreciated - thank you very much!

#
# Apache/PHP/Drupal settings:
#

# Protect files and directories from prying eyes.

Order deny,allow
Allow from all

# Set some options.
Options -Indexes
Options +FollowSymLinks

# Customized error messages.
ErrorDocument 404 /index.php

# Set the default handler.
DirectoryIndex index.php

# Override PHP settings. More in sites/default/settings.php
# but the following cannot be changed at runtime.

# PHP 4, Apache 1

php_value magic_quotes_gpc 0
php_value register_globals 0
php_value session.auto_start 0

# PHP 4, Apache 2

php_value magic_quotes_gpc 0
php_value register_globals 0
php_value session.auto_start 0

# PHP 5, Apache 1 and 2

php_value magic_quotes_gpc 0
php_value register_globals 0
php_value session.auto_start 0

# Reduce the time dynamically generated pages are cache-able.

ExpiresByType text/html A1

# Various rewrite rules.
mod_rewrite on
RewriteEngine on

# If your site can be accessed both with and without the prefix www.
# you can use one of the following settings to force user to use only one option:
#
# If you want the site to be accessed WITH the www. only, adapt and uncomment the following:
# RewriteCond %{HTTP_HOST} !^www\.example\.com$ [NC]
# RewriteRule .* http://www.example.com/ [L,R=301]
#
# If you want the site to be accessed only WITHOUT the www. , adapt and uncomment the following:
# RewriteCond %{HTTP_HOST} !^example\.com$ [NC]
# RewriteRule .* http://example.com/ [L,R=301]

# Modify the RewriteBase if you are using Drupal in a subdirectory and
# the rewrite rules are not working properly.
RewriteBase /

# Rewrite old-style URLs of the form 'node.php?id=x'.
#RewriteCond %{REQUEST_FILENAME} !-f
#RewriteCond %{REQUEST_FILENAME} !-d
#RewriteCond %{QUERY_STRING} ^id=([^&]+)$
#RewriteRule node.php index.php?q=node/view/%1 [L]

# Rewrite old-style URLs of the form 'module.php?mod=x'.
#RewriteCond %{REQUEST_FILENAME} !-f
#RewriteCond %{REQUEST_FILENAME} !-d
#RewriteCond %{QUERY_STRING} ^mod=([^&]+)$
#RewriteRule module.php index.php?q=%1 [L]

# Rewrite rules for static page caching provided by the Boost module
# BOOST START

AddCharset utf-8 .html

RewriteCond %{REQUEST_URI} !^/cache
RewriteCond %{REQUEST_URI} !^/user/login
RewriteCond %{REQUEST_URI} !^/admin
RewriteCond %{HTTP_COOKIE} !DRUPAL_UID
RewriteCond %{REQUEST_METHOD} ^GET$
RewriteCond %{QUERY_STRING} ^$
RewriteCond %{DOCUMENT_ROOT}/cache/%{SERVER_NAME}/0/%{REQUEST_URI} -d
RewriteCond %{DOCUMENT_ROOT}/cache/%{SERVER_NAME}/0/%{REQUEST_URI}/index.html -f
RewriteRule ^(.*)$ cache/%{SERVER_NAME}/0/$1/index.html [L]
RewriteCond %{REQUEST_URI} !^/cache
RewriteCond %{REQUEST_URI} !^/user/login
RewriteCond %{REQUEST_URI} !^/admin
RewriteCond %{HTTP_COOKIE} !DRUPAL_UID
RewriteCond %{REQUEST_METHOD} ^GET$
RewriteCond %{QUERY_STRING} ^$
RewriteCond %{DOCUMENT_ROOT}/cache/%{SERVER_NAME}/0/%{REQUEST_URI}.html -f
RewriteRule ^(.*)$ cache/%{SERVER_NAME}/0/$1.html [L]
# BOOST END

# Rewrite current-style URLs of the form 'index.php?q=x'.
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php?q=$1 [L,QSA]

# $Id: boosted.txt,v 1.4 2006/12/05 10:39:19 arto Exp $