PHP tries to find in:
DOMAIN/company/includes/inc.nav.php
rather than
DOMAIN/includes/inc.nav.php
You'll have to play with .., e.g.
include '../includes/inc.nav.php';
I personally tend to use something like:
include $base_path . 'includes/inc.nav.php';
then at the top set
$base_path = '../';
or if we go further down directory levels,
$base_path = '../../';
etc