but pay attention that after regular ispconfig3 installation,
if you look inside /etc/httpd/conf/httpd.conf
you'll see this setting:
and only in /etc/httpd/conf/sites-available/www.yoursite.com.vhost apache config files there is:
that "enables" .htaccess "looking" by apache.
so that, check if your "/var/www/lockthisfolder"
is configured inside a httpd virtual host with that AllowOverride setting.
i mean the following: