Undefined offset: 0

Fixed it.

function getUserIDandPush($ul){
    global $table_prefix; // Prefix for Database table
    global $user_login;
    global $wpdb; // WordPress WPDB database method 
    $dt = $table_prefix; //Tables Prefix
    if (!is_user_logged_in() && isset($_SERVER['LOGON_USER'])) {
        $as = $wpdb->get_results('SELECT * FROM '.$dt.'users WHERE user_login = "'.$ul.'" ');
        $usID = $as[0]->ID;
        wp_set_current_user($usID, $ul);
        wp_set_auth_cookie($usID);
        do_action('wp_login', $ul);
    }
}