404 error page is not working

0
Hello!
My 404 error page is not working,it redirects to index.php. 🙁
I followed the tutorial on t3 framework, (http://www.t3-framework.org/documentation/bs3-customization#404-page) but still it redirects.
I’m using sef url, so the htaccess.txt is renamed to .htaccess.
A copy of my htaccess.

##
# @package Joomla
# @copyright Copyright (C) 2005 – 2015 Open Source Matters. All rights reserved.
# @license GNU General Public License version 2 or later; see LICENSE.txt
##

##
# READ THIS COMPLETELY IF YOU CHOOSE TO USE THIS FILE!
#
# The line just below this section: ‘Options +FollowSymLinks’ may cause problems
# with some server configurations. It is required for use of mod_rewrite, but may already
# be set by your server administrator in a way that disallows changing it in
# your .htaccess file. If using it causes your server to error out, comment it out (add # to
# beginning of line), reload your site in your browser and test your sef url’s. If they work,
# it has been set by your server administrator and you do not need it set here.
##

## No directory listings
IndexIgnore *

## Can be commented out if causes errors, see notes above.
Options +FollowSymlinks
Options -Indexes

## Mod_rewrite in use.

RewriteEngine On

## Begin – Rewrite rules to block out some common exploits.
# If you experience problems on your site block out the operations listed below
# This attempts to block the most common type of exploit `attempts` to Joomla!
#
# Block out any script trying to base64_encode data within the URL.
RewriteCond %{QUERY_STRING} base64_encode[^(]*([^)]*)
# Block out any script that includes a <script> tag in URL.
RewriteCond %{QUERY_STRING} (<|%3C)([^s]*s)+cript.*(>|%3E) [NC,OR]
# Block out any script trying to set a PHP GLOBALS variable via URL.
RewriteCond %{QUERY_STRING} GLOBALS(=|{0,2})
# Block out any script trying to modify a _REQUEST variable via URL.
RewriteCond %{QUERY_STRING} _REQUEST(=|{0,2})
# Return 403 Forbidden header and show the content of the root homepage
RewriteRule .* index.php [F]
#
## End – Rewrite rules to block out some common exploits.

## Begin – Custom redirects
#
ErrorDocument 404 /error.html
#
## End – Custom redirects

##
# Uncomment following line if your webserver’s URL
# is not directly related to physical file paths.
# Update Your Joomla! Directory (just / for root).
##

# RewriteBase /

## Begin – Joomla! core SEF Section.
#
RewriteRule .* –
#
# If the requested path and file is not /index.php and the request
# has not already been internally rewritten to the index.php script
RewriteCond %{REQUEST_URI} !^/index.php
# and the requested path and file doesn’t directly match a physical file
RewriteCond %{REQUEST_FILENAME} !-f
# and the requested path and file doesn’t directly match a physical folder
RewriteCond %{REQUEST_FILENAME} !-d
# internally rewrite the request to the index.php script
RewriteRule .* index.php [L]
#
## End – Joomla! core SEF Section.

Please help,I need to fix this asap. 🙁