function validate_users() {
    inputs = cssQuery('p.player input');
    is_valid = true;
    for (i=0; i<inputs.length; i++) {
        input = inputs[i];
        if (input.value == '') is_valid = false;
    }

    if (!is_valid) return alert('All fields must be filled.');

    is_valid = true;

    list = cssQuery('p.player');
    for (i=0; i<list.length; i++) {

        player = list[i];
        id = player.getAttribute('id');
        username = cssQuery('p.player#' + id + ' input#' + id + '_username')[0].value;
        password = cssQuery('p.player#' + id + ' input#' + id + '_password')[0].value;

        clsGolfGameWebService.ValidateUser(username, password, function(result) {

            if (result == '0') {

                is_valid = false;

                r = cssQuery('p.player#' + id + ' span.validation');

                if (r.length < 1) {

                    el = document.createElement('span');
                    el.setAttribute('class', 'invalid');
                    el.innerHTML = 'invalid';
                    player.appendChild(el);

                } else {

                    r[0].innerHTML = 'invalid';
                    r[0].setAttribute('class', 'invalid');

                }

            }

        }, AjaxErrorHandler, AjaxTimeOutHandler);

    }

    alert('Validated users.');

    return is_valid;
}