Internal Server Error

Salve a tutti, ho installato magento sul mio sito. Finita la procedura provo ad andare nel backend ma mi segnale questo errore:
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Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, info@altervista.org and inform them of the time the error occurred, and anything you might have done that may have caused the error.
More information about this error may be available in the server error log.
Additionally, a 500 Internal Server Error error was encountered while trying to use an ErrorDocument to handle the request.
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Come lo risolvo?

[Gianluca]

Deve esserci un errore nel file .htaccess che hai caricato, posta qui il contenuto.

Deve esserci un errore nel file .htaccess che hai caricato, posta qui il contenuto.

Salve Gianluca, anche io ho lo stesso errore, posto il contenuto del file .htaccess di seguito:

############################################
## uncomment these lines for CGI mode
## make sure to specify the correct cgi php binary file name
## it might be /cgi-bin/php-cgi

# Action php5-cgi /cgi-bin/php5-cgi
# AddHandler php5-cgi .php

############################################
## GoDaddy specific options

# Options -MultiViews

## you might also need to add this line to php.ini
## cgi.fix_pathinfo = 1
## if it still doesn't work, rename php.ini to php5.ini

############################################
## this line is specific for 1and1 hosting

#AddType x-mapp-php5 .php
#AddHandler x-mapp-php5 .php

############################################
## default index file

DirectoryIndex index.php

<IfModule mod_php5.c>

############################################
## adjust memory limit

# php_value memory_limit 64M
php_value memory_limit 256M
php_value max_execution_time 18000

############################################
## disable magic quotes for php request vars

php_flag magic_quotes_gpc off

############################################
## disable automatic session start
## before autoload was initialized

php_flag session.auto_start off

############################################
## enable resulting html compression

#php_flag zlib.output_compression on

###########################################
# disable user agent verification to not break multiple image upload

php_flag suhosin.session.cryptua off

###########################################
# turn off compatibility with PHP4 when dealing with objects

php_flag zend.ze1_compatibility_mode Off

</IfModule>

<IfModule mod_security.c>
###########################################
# disable POST processing to not break multiple image upload

SecFilterEngine Off
SecFilterScanPOST Off
</IfModule>

<IfModule mod_deflate.c>

############################################
## enable apache served files compression
## http://developer.yahoo.com/performance/rules.html#gzip

# Insert filter on all content
###SetOutputFilter DEFLATE
# Insert filter on selected content types only
#AddOutputFilterByType DEFLATE text/html text/plain text/xml text/css text/javascript

# Netscape 4.x has some problems...
#BrowserMatch ^Mozilla/4 gzip-only-text/html

# Netscape 4.06-4.08 have some more problems
#BrowserMatch ^Mozilla/4\.0[678] no-gzip

# MSIE masquerades as Netscape, but it is fine
#BrowserMatch \bMSIE !no-gzip !gzip-only-text/html

# Don't compress images
#SetEnvIfNoCase Request_URI \.(?:gif|jpe?g|png)$ no-gzip dont-vary

# Make sure proxies don't deliver the wrong content
#Header append Vary User-Agent env=!dont-vary

</IfModule>

<IfModule mod_ssl.c>

############################################
## make HTTPS env vars available for CGI mode

SSLOptions StdEnvVars

</IfModule>

<IfModule mod_rewrite.c>

############################################
## enable rewrites

Options +FollowSymLinks
RewriteEngine on

############################################
## you can put here your magento root folder
## path relative to web root

#RewriteBase /magento/

############################################
## uncomment next line to enable light API calls processing

# RewriteRule ^api/([a-z][0-9a-z_]+)/?$ api.php?type=$1 [QSA,L]

############################################
## rewrite API2 calls to api.php (by now it is REST only)

RewriteRule ^api/rest api.php?type=rest [QSA,L]

############################################
## workaround for HTTP authorization
## in CGI environment

RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]

############################################
## TRACE and TRACK HTTP methods disabled to prevent XSS attacks

RewriteCond %{REQUEST_METHOD} ^TRAC[EK]
RewriteRule .* - [L,R=405]

############################################
## redirect for mobile user agents

#RewriteCond %{REQUEST_URI} !^/mobiledirectoryhere/.*$
#RewriteCond %{HTTP_USER_AGENT} "android|blackberry|ipad|iphone|ipod|iemobile|oper a mobile|palmos|webos|googlebot-mobile" [NC]
#RewriteRule ^(.*)$ /mobiledirectoryhere/ [L,R=302]

############################################
## always send 404 on missing files in these folders

RewriteCond %{REQUEST_URI} !^/(media|skin|js)/

############################################
## never rewrite for existing files, directories and links

RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-l

############################################
## rewrite everything else to index.php

RewriteRule .* index.php [L]

</IfModule>


############################################
## Prevent character encoding issues from server overrides
## If you still have problems, use the second line instead

AddDefaultCharset Off
#AddDefaultCharset UTF-8

<IfModule mod_expires.c>

############################################
## Add default Expires header
## http://developer.yahoo.com/performan...s.html#expires

ExpiresDefault "access plus 1 year"

</IfModule>

############################################
## By default allow all access

Order allow,deny
Allow from all

###########################################
## Deny access to release notes to prevent disclosure of the installed Magento version

<Files RELEASE_NOTES.txt>
order allow,deny
deny from all
</Files>

############################################
## If running in cluster environment, uncomment this
## http://developer.yahoo.com/performance/rules.html#etags

#FileETag none