>
> From error.log:
>
> [Fri Feb 17 12:56:33.478024 2017] [authz_core:error] [pid 5759] [client
> 192.168.160.12:48290] AH01630: client denied by server configuration:
> /usr/share/postfixadmin
So it's an authorisation issue. In your .htaccess file change
Order allow,deny
Allow from all
to the apache 2.4 version
Require all granted
See http://httpd.apache.org/docs/2.4/upgrading.html
P.