Hello Luigi,
Thanks greatly for developing this wonderful plugin!
My Joomla Version= 3.4.4
ReDJ Version=1.7.8
PHP version= 5.5.28

I wasn't having any problem with redirection of bad urls to the custom 404 page of which I had modified the system error.php and replaced in the Protostar template directory until recently when I installed a new template and replaced the custom error.php file in its directory.

Now with the same ReDJ plugin settings (please see the attached screenshot:

), the message I get when I type in a "bad url" to access the 404 page (www.mysite.com/index.php?option=com_content&view=article&id=588) is: This webpage has a redirect loop

After researching, I renamed my .htaccess file and this was the message I had typing a "bad url" : Not Found
The requested URL / 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 have tried all available means but with no success and so, I would very glad if you could help me out here with the below error and details of my .htaccess file where I think there could be a bad REDIRECT RULE set. Thanks very much!

PLEASE NOTE: I HAVE COMMENTED OUT SITENAME AND DATABASENAME FOR SECURITY REASONS

After setting the error reporting to maximum, this is the error I got:
jos-Warning: exception 'RuntimeException' with message 'Deadlock found when trying to get lock; try restarting transaction SQL=INSERT INTO (database name)_redj_errors (`visited_url`, `error_code`, `redirect_url`, `hits`, `last_visit`, `last_referer`) VALUES ('www.mysite.com/index.php?option=com_content&view=article&id=588', '404', '', 1, '2015-09-17 20:33:22', '') ON DUPLICATE KEY UPDATE `hits` = `hits` + 1, `last_visit` = '2015-09-17 20:33:22', `last_referer` = ''' in /home/sitename/public_html/libraries/joomla/database/driver/mysqli.php:610 Stack trace: #0 /home/sitename/public_html/libraries/joomla/database/database.php(33): JDatabaseDriverMysqli->execute() #1 /home/sitename/public_html/plugins/system/redj/redj.php(520): JDatabase->query() #2 /home/sitename/public_html/plugins/system/redj/redj.php(638): plgSystemReDJ::manageError(Object(Exception)) #3 [internal function]: plgSystemReDJ::customError(Object(JException)) #4 /home/sitename/public_html/libraries/legacy/error/error.php(760): call_user_func(Array, Object(JException)) #5 [internal function]: JError::handleCallback(Object(JException), Array) #6 /home/sitename/public_html/libraries/legacy/error/error.php(218): call_user_func_array(Array, Array) #7 /home/sitenamepublic_html/libraries/legacy/error/error.php(179): JError::throwError(Object(JException)) #8 /home/sitenamepublic_html/libraries/legacy/error/error.php(254): JError::raise(1, 404, 'Article not fou...', NULL, true) #9 /home/sitenamepublic_html/components/com_content/models/article.php(169): JError::raiseError(404, 'Article not fou...') #10 /home/sitename/public_html/libraries/legacy/view/legacy.php(401): ContentModelArticle->getItem() #11 /home/sitename/public_html/components/com_content/views/article/view.html.php(42): JViewLegacy->get('Item') #12 /home/sitename/public_html/libraries/legacy/controller/legacy.php(690): ContentViewArticle->display() #13 /home/sitename/public_html/components/com_content/controller.php(104): JControllerLegacy->display(true, Array) #14 /home/sitename/public_html/libraries/legacy/controller/legacy.php(728): ContentController->display() #15 /home/sitename/public_html/components/com_content/content.php(16): JControllerLegacy->execute(NULL) #16 /home/sitename/public_html/libraries/cms/component/helper.php(392): require_once('/home/sitename/p...') #17 /home/sitename/public_html/libraries/cms/component/helper.php(372): JComponentHelper::executeComponent('/home/bigtinz/p...') #18 /home/sitename/public_html/libraries/cms/application/site.php(191): JComponentHelper::renderComponent('com_content') #19 /home/sitename/public_html/libraries/cms/application/site.php(230): JApplicationSite->dispatch() #20 /home/sitename/public_html/libraries/cms/application/cms.php(252): JApplicationSite->doExecute() #21 /home/sitename/public_html/index.php(45): JApplicationCms->execute() #22 {main}

Here are the details of my HTACCESS file:
.....continued below:
### !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! IMPORTANT !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
### !! !!
### !! If you get an Internal Server Error 500 or a blank page when trying !!
### !! to access your site, remove this file and try tweaking its settings !!
### !! in the back-end of the Admin Tools component. !!
### !! !!
### !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
###

##### RewriteEngine enabled - BEGIN
RewriteEngine On
RewriteCond %{HTTP_HOST} ^sitename [NC]
RewriteRule (.*) www.sitename/$1 [L,R=301]
##### RewriteEngine enabled - END

##### RewriteBase set - BEGIN
RewriteBase /
##### RewriteBase set - END

##### File execution order -- BEGIN
DirectoryIndex index.php index.html
##### File execution order -- END

##### No directory listings -- BEGIN
IndexIgnore *
Options -Indexes
##### No directory listings -- END

##### Optimal default expiration time - BEGIN
<IfModule mod_expires.c>
# Enable expiration control
ExpiresActive On

# Default expiration: 1 day after request
ExpiresDefault "now plus 1 day"

# CSS and JS expiration: 1 month after request
ExpiresByType text/css "now plus 1 month"
ExpiresByType application/javascript "now plus 1 month"
ExpiresByType application/x-javascript "now plus 1 month"

# Favicon files expiration: 1 year after request
ExpiresByType image/x-icon "now plus 1 year"
ExpiresByType image/ico "now plus 1 year"
ExpiresByType image/icon "now plus 1 year"
ExpiresByType text/ico "now plus 1 year"
ExpiresByType application/ico "now plus 1 year"

# Gif file expiration: 1 year after request
ExpiresByType image/gif "now plus 1 year"

# Png file expiration: 1 year after request
ExpiresByType image/png "now plus 1 year"

# Image files expiration: 1 month after request
ExpiresByType image/bmp "now plus 1 month"
ExpiresByType image/jpeg "now plus 1 month"
ExpiresByType image/jp2 "now plus 1 month"
ExpiresByType image/pipeg "now plus 1 month"
ExpiresByType image/svg+xml "now plus 1 month"
ExpiresByType image/tiff "now plus 1 month"
ExpiresByType image/vnd.microsoft.icon "now plus 1 month"
ExpiresByType image/vnd.wap.wbmp "now plus 1 month"
ExpiresByType application/vnd.wap.wbxml "now plus 1 month"
ExpiresByType application/smil "now plus 1 month"

# Audio files expiration: 1 month after request
ExpiresByType audio/ogg "now plus 1 month"
ExpiresByType application/ogg "now plus 1 month"
ExpiresByType audio/basic "now plus 1 month"
ExpiresByType audio/mid "now plus 1 month"
ExpiresByType audio/midi "now plus 1 month"
ExpiresByType audio/mpeg "now plus 1 month"
ExpiresByType audio/mp3 "now plus 1 month"
ExpiresByType audio/x-aiff "now plus 1 month"
ExpiresByType audio/x-mpegurl "now plus 1 month"
ExpiresByType audio/x-pn-realaudio "now plus 1 month"
ExpiresByType audio/x-wav "now plus 1 month"

# Movie files expiration: 1 month after request
ExpiresByType application/x-shockwave-flash "now plus 1 month"
ExpiresByType x-world/x-vrml "now plus 1 month"
ExpiresByType video/x-msvideo "now plus 1 month"
ExpiresByType video/mpeg "now plus 1 month"
ExpiresByType video/mp4 "now plus 1 month"
ExpiresByType video/quicktime "now plus 1 month"
ExpiresByType video/x-la-asf "now plus 1 month"
ExpiresByType video/x-ms-asf "now plus 1 month"
</IfModule>
##### Optimal default expiration time - END

##### Common hacking tools and bandwidth hoggers block -- BEGIN
SetEnvIf user-agent "Indy Library" stayout=1
SetEnvIf user-agent "libwww-perl" stayout=1
SetEnvIf user-agent "Download Demon" stayout=1
SetEnvIf user-agent "GetRight" stayout=1
SetEnvIf user-agent "GetWeb!" stayout=1
SetEnvIf user-agent "Go!Zilla" stayout=1
SetEnvIf user-agent "Go-Ahead-Got-It" stayout=1
SetEnvIf user-agent "GrabNet" stayout=1
SetEnvIf user-agent "TurnitinBot" stayout=1
<IfModule !mod_authz_core.c>
deny from env=stayout
</IfModule>
<IfModule mod_authz_core.c>
<RequireAll>
Require all granted
Require not env stayout
</RequireAll>
</IfModule>
##### Common hacking tools and bandwidth hoggers block -- END

##### Automatic compression of resources -- BEGIN
<ifmodule mod_deflate.c>
AddOutputFilterByType DEFLATE text/plain text/xml text/css application/xml application/xhtml+xml application/rss+xml application/javascript application/x-javascript
</ifmodule>
<ifModule mod_gzip.c>
mod_gzip_on Yes
mod_gzip_dechunk Yes
mod_gzip_keep_workfiles No
mod_gzip_can_negotiate Yes
mod_gzip_add_header_count Yes
mod_gzip_send_vary Yes
mod_gzip_min_http 1000
mod_gzip_minimum_file_size 300
mod_gzip_maximum_file_size 512000
mod_gzip_maximum_inmem_size 60000
mod_gzip_handle_methods GET
mod_gzip_item_include file \.(html?|txt|css|js|php|pl|xml|rb|py)$
mod_gzip_item_include mime ^text/plain$
mod_gzip_item_include mime ^text/xml$
mod_gzip_item_include mime ^text/css$
mod_gzip_item_include mime ^application/xml$
mod_gzip_item_include mime ^application/xhtml+xml$
mod_gzip_item_include mime ^application/rss+xml$
mod_gzip_item_include mime ^application/javascript$
mod_gzip_item_include mime ^application/x-javascript$
mod_gzip_item_exclude rspheader ^Content-Encoding:.*gzip.*
mod_gzip_item_include handler ^cgi-script$
mod_gzip_item_include handler ^server-status$
mod_gzip_item_include handler ^server-info$
mod_gzip_item_include handler ^application/x-httpd-php
mod_gzip_item_exclude mime ^image/.*
</ifmodule>
##### Automatic compression of resources -- END
## Force GZip compression for mangled Accept-Encoding headers
<IfModule mod_setenvif.c>
<IfModule mod_headers.c>
SetEnvIfNoCase ^(Accept-EncodXng|X-cept-Encoding|X{15}|~{15}|-{15})$ ^((gzip|deflate)\s*,?\s*)+|[X~-]{4,13}$ HAVE_Accept-Encoding
RequestHeader append Accept-Encoding "gzip,deflate" env=HAVE_Accept-Encoding
</IfModule>
</IfModule>
##### Redirect index.php to / -- BEGIN
RewriteCond %{THE_REQUEST} !^POST
RewriteCond %{THE_REQUEST} ^[A-Z]{3,9}\ /index\.php\ HTTP/
RewriteCond %{SERVER_PORT}>s ^(443>(s)|[0-9]+>s)$
RewriteRule ^index\.php$ http%2://www.sitename.com/ [R=301,L]
##### Redirect index.php to / -- END
##### Redirect non-www to www -- BEGIN
#####RewriteCond %{HTTP_HOST} ^www\.(.+)$ [NC]
#####RewriteRule ^(.*)$ http://%1/$1 [R=301,L]
##### Redirect non-www to www -- END

##### Rewrite rules to block out some common exploits -- BEGIN
RewriteCond %{QUERY_STRING} proc/self/environ [OR]
RewriteCond %{QUERY_STRING} mosConfig_[a-zA-Z_]{1,21}(=|\%3D) [OR]
RewriteCond %{QUERY_STRING} base64_(en|de)code\(.*\) [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]
##### Rewrite rules to block out some common exploits -- END
##### File injection protection -- BEGIN
RewriteCond %{REQUEST_METHOD} GET
RewriteCond %{QUERY_STRING} [a-zA-Z0-9_]=http:// [OR]
RewriteCond %{QUERY_STRING} [a-zA-Z0-9_]=(\.\.//?)+ [OR]
RewriteCond %{QUERY_STRING} [a-zA-Z0-9_]=/([a-z0-9_.]//?)+ [NC]
RewriteRule .* - [F]
##### File injection protection -- END

##### Advanced server protection rules exceptions -- BEGIN
RewriteRule ^administrator\/components\/com_akeeba\/restore\.php$ - [L]
RewriteRule ^administrator\/components\/com_admintools\/restore\.php$ - [L]
RewriteRule ^administrator\/components\/com_joomlaupdate\/restore\.php$ - [L]
RewriteRule ^templates\/your_template_name_here/ - [L]
##### Advanced server protection rules exceptions -- END

##### Advanced server protection -- BEGIN

RewriteCond %{QUERY_STRING} \=PHP[a-f0-9]{8}-[a-f0-9]{4}-[a-f0-9]{4}-[a-f0-9]{4}-[a-f0-9]{12} [NC]
RewriteRule .* - [F]
## Back-end protection
RewriteRule ^administrator/?$ - [L]
RewriteRule ^administrator/index\.(php|html?)$ - [L]
RewriteRule ^administrator/index[23]\.php$ - [L]
RewriteRule ^administrator/(components|modules|templates|images|plugins)/.*\.(jpe|jpg|jpeg|jp2|jpe2|png|gif|bmp|css|js|swf|html|mpg|mp3|mpeg|mp4|avi|wav|ogg|ogv|xls|xlsx|doc|docx|ppt|pptx|zip|rar|pdf|xps|txt|7z|svg|odt|ods|odp|flv|mov|htm|ttf|woff|eot)$ - [L]
RewriteRule ^administrator/ - [F]
## Allow limited access for certain Joomla! system directories with client-accessible content
RewriteRule ^(components|modules|templates|images|plugins|media|libraries|media/jui/fonts)/.*\.(jpe|jpg|jpeg|jp2|jpe2|png|gif|bmp|css|js|swf|html|mpg|mp3|mpeg|mp4|avi|wav|ogg|ogv|xls|xlsx|doc|docx|ppt|pptx|zip|rar|pdf|xps|txt|7z|svg|odt|ods|odp|flv|mov|ico|htm|ttf|woff|eot|xml)$ - [L]
RewriteRule ^(components|modules|templates|images|plugins|media|libraries|media/jui/fonts)/ - [F]
## Disallow front-end access for certain Joomla! system directories (unless access to their files is allowed above)
RewriteRule ^includes/js/ - [L]
RewriteRule ^(cache|includes|language|logs|log|tmp)/ - [F]
RewriteRule ^(configuration\.php|CONTRIBUTING\.md|htaccess\.txt|joomla\.xml|LICENSE\.txt|phpunit\.xml|README\.txt|web\.config\.txt) - [F]

## Disallow access to rogue PHP files throughout the site, unless they are explicitly allowed
RewriteCond %{REQUEST_FILENAME} (\.php)$
RewriteCond %{REQUEST_FILENAME} !(/index[23]?\.php)$
RewriteCond %{REQUEST_FILENAME} -f
RewriteRule (.*\.php)$ - [F]
## Disallow access to htaccess.txt, php.ini and configuration.php-dist
RewriteRule ^(htaccess\.txt|configuration\.php-dist|php\.ini)$ - [F]
## Protect against clickjacking
<IfModule mod_headers.c>

Header always append X-Frame-Options SAMEORIGIN

# The `X-Frame-Options` response header should be send only for
# HTML documents and not for the other resources.

<FilesMatch "\.(appcache|atom|bbaw|bmp|crx|css|cur|eot|f4[abpv]|flv|geojson|gif|htc|ico|jpe?g|js|json(ld)?|m4[av]|manifest|map|mp4|oex|og[agv]|opus|otf|pdf|png|rdf|rss|safariextz|svgz?|swf|topojson|tt[cf]|txt|vcard|vcf|vtt|webapp|web[mp]|woff2?|xloc|xml|xpi)$">
Header unset X-Frame-Options
</FilesMatch>

</IfModule>
## Reduce MIME type security risks
<IfModule mod_headers.c>
Header set X-Content-Type-Options "nosniff"
</IfModule>
## Reflected XSS prevention
<IfModule mod_headers.c>
Header set X-XSS-Protection "1; mode=block"
</IfModule>

# mod_headers cannot match based on the content-type, however,
# the X-XSS-Protection response header should be send only for
# HTML documents and not for the other resources.

<IfModule mod_headers.c>
<FilesMatch "\.(appcache|atom|bbaw|bmp|crx|css|cur|eot|f4[abpv]|flv|geojson|gif|htc|ico|jpe?g|js|json(ld)?|m4[av]|manifest|map|mp4|oex|og[agv]|opus|otf|pdf|png|rdf|rss|safariextz|svgz?|swf|topojson|tt[cf]|txt|vcard|vcf|vtt|webapp|web[mp]|webmanifest|woff2?|xloc|xml|xpi)$">
Header unset X-XSS-Protection
</FilesMatch>
</IfModule>
## Remove Apache and PHP version signature
<IfModule mod_headers.c>
Header unset X-Powered-By
</IfModule>

ServerSignature Off
## Prevent content transformation
<IfModule mod_headers.c>
Header merge Cache-Control "no-transform"
</IfModule>
##### Advanced server protection -- END

## Set the UTF-8 character set as the default
# Serve all resources labeled as `text/html` or `text/plain`
# with the media type `charset` parameter set to `UTF-8`.

AddDefaultCharset utf-8

# Serve the following file types with the media type `charset`
# parameter set to `UTF-8`.
#
# httpd.apache.org/docs/current/mod/mod_mime.html#addcharset

<IfModule mod_mime.c>
AddCharset utf-8 .atom \
.bbaw \
.css \
.geojson \
.js \
.json \
.jsonld \
.rdf \
.rss \
.topojson \
.vtt \
.webapp \
.xloc \
.xml
</IfModule>
##### Joomla! core SEF Section -- BEGIN
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
RewriteCond %{REQUEST_URI} !^/index\.php
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule .* index.php [L]
##### Joomla! core SEF Section -- END



<Files ~ "sitemap\.xml$">
Order allow,deny
Allow from all
</Files>

<Files ~ "six\.xml$">
Order allow,deny
Allow from all
</Files>

FileETag None

RewriteRule ^sitemap.xml$ index.php?option=com_osmap&view=xml&tmpl=component&id=1 [L]

suPHP_ConfigPath /home/sitename/public_html

Hello Luigi,

Thanks very much for your response!

Please, I have replied to the above email as you have requested with more details. Thanks once again and waiting for a response!

Hello Luigi,

Thanks very much for your response. Okay and waiting!

Thanks once again!