I resolved this issue by following instructions here: https://www.ads-software.com/support/topic/unable-to-access-the-settings-page-1
The root cause seems to be that Windows was using backslashes for directory path. In wp-includes/vars.php, it has the following line:-
preg_match(‘#/wp-admin/?(.*?)$#i’, $_SERVER[‘PHP_SELF’], $self_matches);
Problem solved by adding this line:-
$_SERVER[‘PHP_SELF’] = str_replace(‘\\’, ‘/’, $_SERVER[‘PHP_SELF’]);
Just before:-
require_once(ABSPATH . ‘wp-settings.php’);
In your wp-config.php.