Upload privacy not working

Hello,

I am trying to build a private site. One of the most important aspects of the site consists in the uploads, and they definitely need to be private.

I found a very interesting topic on that here: http://wordpress.stackexchange.com/questions/37144/how-to-protect-uploads-if-user-is-not-logged-in.The thing is that this solution does not work for me, and I do not know why. For the moment, I am trying my website on my computer, with an apache server. I put my .htaccess just here:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ – [L]
RewriteCond %{REQUEST_FILENAME} -s
RewriteRule ^wp-content/uploads/(.*)$ dl-file.php?file=$1 [QSA,
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress

and the dl-file.html, as given here: https://gist.github.com/1552239

my uploads are located either just under /wp-content/uploads or in a subdirectory of this directory. I would like to know if there is a way of diagnosing, or see where the does the problem come from. I have deactivated all the plugins, in vain.

Thanks!