Errore 500 a tratti

Scusate, e' un po' di tempo che a volte mi compare questo errore quando accedo al mio sito. Non capisco a cosa e' dovuto visto che sono settimane che non effettuo modifiche..
Qualcuno mi puo' aiutare a capire?


Errore 500 :(

Si è verificato un errore.

Questo errore può presentarsi a causa di un file .htaccess sintatticamente scorretto, inserito da te o da un tuo script nella cartella corrente.

Per tornare ad accedere via browser ai contenuti della cartella devi apire la gestione files nel pannello di controllo, cliccare sull'icona raffigurante i due ingranaggi e correggere o eliminare (lasciando il testo bianco) il file. Per maggiori informazioni sulle direttive supportate dai files .htaccess consulta l'help online sempre all'interno del pannello di controllo.

Segue il contenuto di .htaccess

# @license http://www.gnu.org/copyleft/gpl.html GNU/GPL
# Joomla! is Free Software
##


################################################## ###
# 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 dissallows 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.
#
################################################## ###

## Can be commented out if causes errors, see notes above.
Options +FollowSymLinks

#
# 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!
#
## Deny access to extension xml files (uncomment out to activate)
#<Files ~ "\.xml$">
#Order allow,deny
#Deny from all
#Satisfy all
#</Files>
## End of deny access to extension xml files

RewriteCond %{QUERY_STRING} mosConfig_[a-zA-Z_]{1,21}(=|\%3D) [OR]
# Block out any script trying to base64_encode crap to send via URL
RewriteCond %{QUERY_STRING} base64_encode.*\(.*\) [OR]
# Block out any script that includes a <script> tag in URL
RewriteCond %{QUERY_STRING} (\<|%3C).*script.*(\>|%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})
# Send all blocked request to homepage with 403 Forbidden error!
RewriteRule ^(.*)$ index.php [F,L]
#
########## End - Rewrite rules to block out some common exploits

# 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
#
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} !^/index.php
RewriteCond %{REQUEST_URI} (/|\.php|\.html|\.htm|\.feed|\.pdf|\.raw|/[^.]*)$ [NC]
RewriteRule (.*) index.php
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization},L]
#
########## End - Joomla! core SEF Section

# # av:php5-engine
AddHandler av-php5 .php


# av:PHP-upload
php_value upload_max_filesize 10M
php_value post_max_size 10M
php_value max_input_time 300
# PHP-upload

# av:AntiHotlink
RewriteEngine on
RewriteBase /
RewriteCond %{REQUEST_URI} \.(gif|jpe?g|png)$ [NC]
RewriteCond %{HTTP_REFERER} !^$
RewriteCond %{HTTP_REFERER} !^http://([a-z0-9\-\.]*)altene\.altervista\.org
RewriteCond %{REQUEST_URI} !^\/_altervista_ht\/
RewriteCond %{HTTP_REFERER} !^http://([a-z0-9\-\.]+)google\.
RewriteRule .*$ http://hl.altervista.org/split.php?http://%{HTTP_HOST}%{REQUEST_URI} [R,L]
# AntiHotlink