Do you allow symlinks and use the -l flag? Are you on HTTPS? Maybe # the line with the -f flag so it doesn't test the symlinks and just accepts it?
Put in your .htaccess:
Code:
RewriteEngine On
# enable symbolic links
Options +FollowSymLinks
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-l
RewriteRule ^(.+) index.php [L]