may be a ownership problem.
try do
chmod -R 775 /var/www/folder
and/or
chown -R domain:www-data /var/www/folder
- where domain is the user of that particular virtualhost or www-data
for directory listing you may want to modify in /etc/apache2/sites-available/default
+Indexes
see http://www.cyberciti.biz/faq/enabling-apache-file-directory-indexing/