Err: Client denied by server configuration after Apache upgrade

From Apache 2.4, syntax of user directive options were changed. So that Apache configuration from old version to new 2.4 or later will cause this error due the incorrect syntax.

# Apache version 2.2 or lower configuration:
<Directory /docroot>
Order allow,deny
Allow from all
</Directory>

# Apacheversion 2.4 or later configuration:
<Directory /docroot>
Require all granted
</Directory>

For more information on new syntax visit Apache Access Directive in Details.

So use latest directory access directives syntax to avoid the same type of errors.