phpPgAdmin - postgres - error "Login disallowed for security reasons"

PhpPgAdmin  by default deny access for certain usernames (pgsql, postgres, root, administrator) , Also it will block any attempt to login using no password .

The line controlling this is in the  config.inc.php file

$conf['extra_login_security'] = true;

If you are developing a website locally you can change this option in config.inc.php file to false but keep in mind that this option is a very good security helper if you are in production phase.