Hello.
I'm using K2 v2.6.5 and Joomla 2.5.22

I encountered a problem with this rule in htaccess:

RewriteRule .* index.php [F]

When the line is commented out, everething seems fine, but it's very important not to do this for me. In this way k2.css and k2.js in backend of my site not loaded with this error:

Failed to load resource: the server responded with a status of 403 (Forbidden)

You can see it in sreenshot. Thx and sorry for my bad english.

Are you using any custom .htaccess protection?
Any security extensions?

Yes, i use some derectives from master htaccess protection: docs.joomla.org/Htaccess_examples_%28security%29

No security extensions used by me.

Thx, for fast reply.

Here is the full .htaccess file, failed to put under spoiler sorry:

IndexIgnore *
Options +FollowSymLinks All -Indexes

## Mod_rewrite in use.

RewriteEngine On

########## Begin - File execution order, by Komra.de
DirectoryIndex index.php index.html
########## End - File execution order

## Удаляем .html c конца URL
RewriteRule ^index.html$ / [R=301,L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} \.html$
RewriteRule ^(.*)\.html$ /$1 [R,L]
## Удаляем .html c конца URL

RewriteCond %{HTTP_HOST} ^mysite\.ru
RewriteRule ^(.*)$ www.mysite.ru/$1 [R=permanent,L]

## Фильтруем кавычки в url
RewriteRule ^(.*) /$1 [R=301,L]
## Фильтруем кавычки в url

## Удаляем слеш с конца урл
RewriteCond %{REQUEST_URI} ^.*/$ [NC]
RewriteCond %{REQUEST_URI} !^/administrator
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)/$ /$1 [L,R=301]
## Удаляем слеш с конца урл

<IfModule mod_gzip.c>
mod_gzip_on Yes
mod_gzip_dechunk Yes
mod_gzip_item_include file \.(html?|txt|css|js|php)$
mod_gzip_item_include mime ^text/.*
mod_gzip_item_include mime ^application/x-javascript.*
mod_gzip_item_exclude mime ^image/.*
mod_gzip_item_exclude rspheader ^Content-Encoding:.*gzip.*
</IfModule>

########## Begin - Add optional bad user agent or IP blocking code
#
# If you need to block certain user agents or IP addresses and
# other signatures, place that code here. Ensure the rules use
# the correct RewriteRule syntax and the [F] flag.
#
########## End - Add optional bad user agent or IP blocking code

########## 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!
#
# If the request query string contains /proc/self/environ (by SigSiu.net)
RewriteCond %{QUERY_STRING} proc/self/environ [OR]
# Block out any script trying to set a mosConfig value through the URL
# (these attacks wouldn't work w/out Joomla! 1.5's Legacy Mode plugin)
RewriteCond %{QUERY_STRING} mosConfig_[a-zA-Z_]{1,21}(=|\%3D) [OR]
# Block out any script trying to base64_encode or base64_decode data within the URL
RewriteCond %{QUERY_STRING} base64_(en|de)code[^(]*\([^)]*\) [OR]
## IMPORTANT: If the above line throws an HTTP 500 error, replace it with these 2 lines:
# RewriteCond %{QUERY_STRING} base64_encode\(.*\) [OR]
# RewriteCond %{QUERY_STRING} base64_decode\(.*\) [OR]
# 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(=|\[|\%[0-9A-Z]{0,2}) [OR]
# Block out any script trying to modify a _REQUEST variable via URL
RewriteCond %{QUERY_STRING} _REQUEST(=|\[|\%[0-9A-Z]{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 - File injection protection, by SigSiu.net
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]
########## End - File injection protection

########## Begin - Basic antispam Filter, by SigSiu.net
## I removed some common words, tweak to your liking
## This code uses PCRE and works only with Apache 2.x.
## This code will NOT work with Apache 1.x servers.
RewriteCond %{QUERY_STRING} \b(ambien|blue\spill|cialis|cocaine|ejaculation|erectile)\b [NC,OR]
RewriteCond %{QUERY_STRING} \b(erections|hoodia|huronriveracres|impotence|levitra|libido)\b [NC,OR]
RewriteCond %{QUERY_STRING} \b(lipitor|phentermin|pro[sz]ac|sandyauer|tramadol|troyhamby)\b [NC,OR]
RewriteCond %{QUERY_STRING} \b(ultram|unicauca|valium|viagra|vicodin|xanax|ypxaieo)\b [NC]
## Note: The final RewriteCond must NOT use the [OR] flag.
RewriteRule .* - [F]
## Note: The previous lines are a "compressed" version
## of the filters. You can add your own filters as:
## RewriteCond %{QUERY_STRING} \bbadword\b [NC,OR]
## where "badword" is the word you want to exclude.
########## End - Basic antispam Filter, by SigSiu.net

########## Begin - Advanced server protection - query strings, referrer and config
# Advanced server protection, version 3.2 - May 2011
# by Nicholas K. Dionysopoulos

## Disallow PHP Easter Eggs (can be used in fingerprinting attacks to determine
## your PHP version). See www.0php.com/php_easter_egg.php and
## osvdb.org/12184 for more information
RewriteCond %{QUERY_STRING} \=PHP[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12} [NC]
RewriteRule .* - [F]

## SQLi first line of defense, thanks to Radek Suski (SigSiu.net) @
## www.sigsiu.net/presentations/fortifying_your_joomla_website.html
## May cause problems on legitimate requests
RewriteCond %{QUERY_STRING} concat[^\(]*\( [NC,OR]
RewriteCond %{QUERY_STRING} union([^s]*s)+elect [NC,OR]
RewriteCond %{QUERY_STRING} union([^a]*a)+ll([^s]*s)+elect [NC]
RewriteRule .* - [F]

## Referrer filtering for common media files. Replace with your own domain name.
## This blocks most common fingerprinting attacks ;)
## Note: Change www\.example\.com with your own domain name, substituting the
## dots with \. i.e. use www\.example\.com for www.example.com
RewriteRule ^(images/stories/([^.]+)\.(jpe[g2]?|jpg|png|gif|bmp|css|js|swf|ico|html?))$ - [L]
RewriteCond %{HTTP_REFERER} .
RewriteCond %{HTTP_REFERER} !^https?://(www\.)?mysite\.ru [NC]
RewriteCond %{REQUEST_FILENAME} -f
RewriteRule \.(jp(e?g|2)?|png|gif|bmp|css|js|swf|ico)$ - [F]

## Disallow visual fingerprinting of Joomla! sites (module position dump)
## Initial idea by Brian Teeman and Ken Crowder, see:
## www.slideshare.net/brianteeman/hidden-joomla-secrets
## Improved by @nikosdion to work more efficiently and handle template
## and tmpl query parameters
RewriteCond %{QUERY_STRING} (^|&)tmpl=(component|system) [NC]
RewriteRule .* - [L]
RewriteCond %{QUERY_STRING} (^|&)t(p|emplate|mpl)= [NC]
RewriteRule .* - [F]

## Disallow access to htaccess.txt, configuration.php, configuration.php-dist and php.ini
RewriteRule ^(htaccess\.txt|configuration\.php(-dist)?|php\.ini)$ - [F]

########## End - Advanced server protection - query strings, referrer and config

########## Begin - Advanced server protection rules exceptions ####
##
## These are sample exceptions to the Advanced Server Protection 3.1
## rule set further down this file.
##
## Allow UddeIM CAPTCHA
##RewriteRule ^components/com_uddeim/captcha15\.php$ - [L]
## Allow Phil Taylor's Turbo Gears
##RewriteRule ^plugins/system/GoogleGears/gears-manifest\.php$ - [L]
## Allow JoomlaWorks AllVideos
##RewriteRule ^plugins/content/jw_allvideos/includes/jw_allvideos_scripts\.php$ - [L]
## Allow Admin Tools Joomla! updater to run
##RewriteRule ^administrator/components/com_admintools/restore\.php$ - [L]
## Allow Akeeba Backup Professional's integrated restoration script to run
##RewriteRule ^administrator/components/com_akeeba/restore\.php$ - [L]
## Allow Akeeba Kickstart
##RewriteRule ^kickstart\.php$ - [L]

# Add more rules to single PHP files here

## Allow Agora attachments, but not PHP files in that directory!
##RewriteCond %{REQUEST_FILENAME} !(\.php)$
##RewriteCond %{REQUEST_FILENAME} -f
##RewriteRule ^components/com_agora/img/members/ - [L]

# Add more rules for allowing full access (except PHP files) on more directories here

## Uncomment to allow full access to the cache directory (strongly not recommended!)
#RewriteRule ^cache/ - [L]
## Uncomment to allow full access to the tmp directory (strongly not recommended!)
#RewriteRule ^tmp/ - [L]

# Add more full access rules here

########## End - Advanced server protection rules exceptions ####

########## Begin - Advanced server protection - paths and files
# Advanced server protection, version 3.2 - May 2011
# by Nicholas K. Dionysopoulos

## Back-end protection
## This also blocks fingerprinting attacks browsing for XML and INI files
RewriteRule ^administrator/?$ - [L]
RewriteRule ^administrator/index\.(php|html?)$ - [L]
RewriteRule ^administrator/index[23]\.php$ - [L]
RewriteRule ^administrator/(components|modules|templates|images|plugins)/([^/]+/)*([^/.]+\.)+(jp(e?g|2)?|png|gif|bmp|css|js|ico|swf|html?|mp(eg?|[34])|avi|wav|og[gv]|xlsx?|docx?|pptx?|zip|rar|pdf|xps|txt|7z|svg|od[tsp]|flv|mov)$ - [L]
RewriteRule ^administrator/ - [F]

## Explicitly allow access only to XML-RPC's xmlrpc/index.php or plain xmlrpc/ directory
RewriteRule ^xmlrpc/(index\.php)?$ - [L]
RewriteRule ^xmlrpc/ - [F]

## Disallow front-end access for certain Joomla! system directories
RewriteRule ^includes/js/ - [L]
RewriteRule ^(includes|language|libraries|logs|tmp)/ - [F]

## Allow limited access for certain Joomla! system directories with client-accessible content
RewriteRule ^(components|modules|plugins|templates)/([^/]+/)*([^/.]+\.)+(jp(e?g|2)?|png|gif|bmp|css|js|ico|swf|html?|mp(eg?|[34])|avi|wav|og[gv]|xlsx?|docx?|pptx?|zip|rar|pdf|xps|txt|7z|svg|od[tsp]|flv|mov)$ - [L]
## Uncomment this line if you have extensions which require direct access to their own
## custom index.php files. Note that this is UNSAFE and the developer should be ashamed
## for being so lame, lazy and security unconscious.
# RewriteRule ^(components|modules|plugins|templates)/([^/]+/)*(index\.php)?$ - [L]
## Uncomment the following line if your template requires direct access to PHP files
## inside its directory, e.g. GZip compressed copies of its CSS files
# RewriteRule ^templates/([^/]+/)*([^/.]+\.)+php$ - [L]
RewriteRule ^(components|modules|plugins|templates)/ - [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$
## The next line is to explicitly allow the forum post assistant(fpa-xx)script to run
RewriteCond %{REQUEST_FILENAME} !/fpa-[a-z]{2}\.php
RewriteCond %{REQUEST_FILENAME} -f
RewriteRule ^([^/]+/)*([^/.]+\.)+php$ - [F]

########## End - Advanced server protection - paths and files

########## Begin - Google Apps redirection, by Komra.de
## Uncomment the following line to enable:
# RewriteRule ^mail mail.google.com/a/example.com [R=301,L]
## If the above doesn't work on your server, try this:
## RewriteRule ^mail mail.google.com/a/example.com [R,L]
########## End - Google Apps redirection

########## Begin - Redirect index.php to /
## Note: Change example.com to reflect your own domain name
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.mysite.ru/$1 [R=301,L]
## If the above line throws a 500 error, change [R=301,L] to [R,L]
########## End - Redirect index.php to /

########## Begin - Joomla! core SEF Section
#
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
#
# 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 request is for the site root, or for an extensionless URL,
# or the requested URL ends with one of the listed extensions
RewriteCond %{REQUEST_URI} /component/|(/[^.]*|\.(php|html?|feed|pdf|vcf|raw|ini|zip|json|file))$ [NC]
# and the requested path and file doesn't directly match a physical file
RewriteCond %{REQUEST_FILENAME} !-f
# and the requested path 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

ServerSignature Off

RewriteCond %{REQUEST_METHOD} ^(HEAD|TRACE|DELETE|TRACK) [NC,OR]
RewriteCond %{THE_REQUEST} (\\r|\\n|%0A|%0D) [NC,OR]

RewriteCond %{HTTP_USER_AGENT} ^$ [OR]
RewriteCond %{HTTP_USER_AGENT} ^(java|curl|wget) [NC,OR]
RewriteCond %{HTTP_USER_AGENT} (winhttp|HTTrack|clshttp|archiver|loader|email|harvest|extract|grab|miner) [NC,OR]
RewriteCond %{HTTP_USER_AGENT} (libwww-perl|curl|wget|python|nikto|scan) [NC,OR]
RewriteCond %{HTTP_USER_AGENT} (<|>|’|%0A|%0D|%27|%3C|%3E|%00) [NC,OR]

#Block mySQL injects
RewriteCond %{QUERY_STRING} (;|<|>|’|”|\)|%0A|%0D|%22|%27|%3C|%3E|%00).*(/\*|union|select|insert|cast|set|declare|drop|update|md5|benchmark) [NC,OR]

RewriteCond %{QUERY_STRING} \.\./\.\. [OR]

RewriteCond %{QUERY_STRING} (localhost|loopback|127\.0\.0\.1) [NC,OR]
RewriteCond %{QUERY_STRING} \.[a-z0-9] [NC,OR]
RewriteCond %{QUERY_STRING} (<|>|’|%0A|%0D|%27|%3C|%3E|%00) [NC]
# Note: The final RewriteCond must NOT use the [OR] flag.

# Return 403 Forbidden error.
RewriteRule .* index.php [F]

AddDefaultCharset utf-8

php_value max_execution_time 180
php_value memory_limit 512M

ErrorDocument 404 www.mysite.ru/error404



########## Block bad user agents
## The following list may include bots that no longer exist or are not a problem
## for your site. The list will always be incomplete and it is therefore wise to
## follow discussions on one of the many "security" mailing lists or on a forum
## such as www.webmasterworld.com/search_engine_spiders/
## It is also unwise to rely on this list as your ONLY security mechanism.
RewriteCond %{HTTP_USER_AGENT} ^BlackWidow [OR]
RewriteCond %{HTTP_USER_AGENT} ^Bot\ This email address is being protected from spambots. You need JavaScript enabled to view it. [OR]
RewriteCond %{HTTP_USER_AGENT} ^ChinaClaw [OR]
RewriteCond %{HTTP_USER_AGENT} ^Custo [OR]
RewriteCond %{HTTP_USER_AGENT} ^DISCo [OR]
RewriteCond %{HTTP_USER_AGENT} ^Download\ Demon [OR]
RewriteCond %{HTTP_USER_AGENT} ^eCatch [OR]
RewriteCond %{HTTP_USER_AGENT} ^EirGrabber [OR]
RewriteCond %{HTTP_USER_AGENT} ^EmailSiphon [OR]
RewriteCond %{HTTP_USER_AGENT} ^EmailWolf [OR]
RewriteCond %{HTTP_USER_AGENT} ^Express\ WebPictures [OR]
RewriteCond %{HTTP_USER_AGENT} ^ExtractorPro [OR]
RewriteCond %{HTTP_USER_AGENT} ^EyeNetIE [OR]
RewriteCond %{HTTP_USER_AGENT} ^FlashGet [OR]
RewriteCond %{HTTP_USER_AGENT} ^GetRight [OR]
RewriteCond %{HTTP_USER_AGENT} ^GetWeb! [OR]
RewriteCond %{HTTP_USER_AGENT} ^Go!Zilla [OR]
RewriteCond %{HTTP_USER_AGENT} ^Go-Ahead-Got-It [OR]
RewriteCond %{HTTP_USER_AGENT} ^GrabNet [OR]
RewriteCond %{HTTP_USER_AGENT} ^Grafula [OR]
RewriteCond %{HTTP_USER_AGENT} ^HMView [OR]
RewriteCond %{HTTP_USER_AGENT} HTTrack [NC,OR]
RewriteCond %{HTTP_USER_AGENT} ^Image\ Stripper [OR]
RewriteCond %{HTTP_USER_AGENT} ^Image\ Sucker [OR]
RewriteCond %{HTTP_USER_AGENT} Indy\ Library [NC,OR]
RewriteCond %{HTTP_USER_AGENT} ^InterGET [OR]
RewriteCond %{HTTP_USER_AGENT} ^Internet\ Ninja [OR]
RewriteCond %{HTTP_USER_AGENT} ^JetCar [OR]
RewriteCond %{HTTP_USER_AGENT} ^JOC\ Web\ Spider [OR]
RewriteCond %{HTTP_USER_AGENT} ^larbin [OR]
RewriteCond %{HTTP_USER_AGENT} ^LeechFTP [OR]
RewriteCond %{HTTP_USER_AGENT} ^Mass\ Downloader [OR]
RewriteCond %{HTTP_USER_AGENT} ^MIDown\ tool [OR]
RewriteCond %{HTTP_USER_AGENT} ^Mister\ PiX [OR]
RewriteCond %{HTTP_USER_AGENT} ^Navroad [OR]
RewriteCond %{HTTP_USER_AGENT} ^NearSite [OR]
RewriteCond %{HTTP_USER_AGENT} ^NetAnts [OR]
RewriteCond %{HTTP_USER_AGENT} ^NetSpider [OR]
RewriteCond %{HTTP_USER_AGENT} ^Net\ Vampire [OR]
RewriteCond %{HTTP_USER_AGENT} ^NetZIP [OR]
RewriteCond %{HTTP_USER_AGENT} ^Octopus [OR]
RewriteCond %{HTTP_USER_AGENT} ^Offline\ Explorer [OR]
RewriteCond %{HTTP_USER_AGENT} ^Offline\ Navigator [OR]
RewriteCond %{HTTP_USER_AGENT} ^PageGrabber [OR]
RewriteCond %{HTTP_USER_AGENT} ^Papa\ Foto [OR]
RewriteCond %{HTTP_USER_AGENT} ^pavuk [OR]
RewriteCond %{HTTP_USER_AGENT} ^pcBrowser [OR]
RewriteCond %{HTTP_USER_AGENT} ^RealDownload [OR]
RewriteCond %{HTTP_USER_AGENT} ^ReGet [OR]
RewriteCond %{HTTP_USER_AGENT} ^SiteSnagger [OR]
RewriteCond %{HTTP_USER_AGENT} ^SmartDownload [OR]
RewriteCond %{HTTP_USER_AGENT} ^SuperBot [OR]
RewriteCond %{HTTP_USER_AGENT} ^SuperHTTP [OR]
RewriteCond %{HTTP_USER_AGENT} ^Surfbot [OR]
RewriteCond %{HTTP_USER_AGENT} ^tAkeOut [OR]
RewriteCond %{HTTP_USER_AGENT} ^Teleport\ Pro [OR]
RewriteCond %{HTTP_USER_AGENT} ^VoidEYE [OR]
RewriteCond %{HTTP_USER_AGENT} ^Web\ Image\ Collector [OR]
RewriteCond %{HTTP_USER_AGENT} ^Web\ Sucker [OR]
RewriteCond %{HTTP_USER_AGENT} ^WebAuto [OR]
RewriteCond %{HTTP_USER_AGENT} ^WebCopier [OR]
RewriteCond %{HTTP_USER_AGENT} ^WebFetch [OR]
RewriteCond %{HTTP_USER_AGENT} ^WebGo\ IS [OR]
RewriteCond %{HTTP_USER_AGENT} ^WebLeacher [OR]
RewriteCond %{HTTP_USER_AGENT} ^WebReaper [OR]
RewriteCond %{HTTP_USER_AGENT} ^WebSauger [OR]
RewriteCond %{HTTP_USER_AGENT} ^Website\ eXtractor [OR]
RewriteCond %{HTTP_USER_AGENT} ^Website\ Quester [OR]
RewriteCond %{HTTP_USER_AGENT} ^WebStripper [OR]
RewriteCond %{HTTP_USER_AGENT} ^WebWhacker [OR]
RewriteCond %{HTTP_USER_AGENT} ^WebZIP [OR]
RewriteCond %{HTTP_USER_AGENT} ^Widow [OR]
RewriteCond %{HTTP_USER_AGENT} ^WWWOFFLE [OR]
RewriteCond %{HTTP_USER_AGENT} ^Xaldon\ WebSpider [OR]
RewriteCond %{HTTP_USER_AGENT} ^Zeus
## Note: The final RewriteCond must NOT use the [OR] flag.

## Return 403 Forbidden error.
RewriteRule .* - [F]

Did you replace all the mysite.com and example.com with the actual address/

If yes block out all the blocks containing rules about css and js blocking.

Yes, i replace mysite with my actual address.

Comenting all lines which have css and js properties, not solve my problem.

Only without this rule RewriteRule .* index.php [F] everything good.

This file is from 2011 and a lot of things may have changed from then.
If commenting out blocks does not work, then you should look for another solution.

There are several links posted on the page you sent me.