[Plugin: WP Supercache] Mod Rewrite rules cannot be updated!

Hi,
I have just installed wordpress on CentOS shared hosting (location: /www/wordpress/). I have downloaded and activated wp supercache but in ‘Advanced’ tab, it displays:

You must have BEGIN and END markers in /.htaccess for the auto update to work. They look like this and surround the main WordPress mod_rewrite rules
#BEGIN WordPress
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
# END WordPress
Refresh this page when you have updated your .htaccess file.

The problem is that the content of my .htaccess (location: /wordpress/.htaccess) is:
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /wordpress/
RewriteRule ^index\.php$ – [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /wordpress/index.php [L]
</IfModule>

Where’s the problem? I’ve tried to comment the elseif that displays that error and plugin showed the code that i could paste into .htaccess. I have done it but supercache hasn’t recognized it.
Can you help me? Thank you very much!
Excuse me for the English, but I’m Italian 🙂