SyntaxError: Unexpected token ( in JSON at position 0

mau nanya mas ini ane ada form login pas masukin username:password dengan benar trus klik login muncul json error kek gni: SyntaxError: Unexpected token ( in JSON at position 0 muncul pesan itu bukan berarti gagal si form login nya harus di refresh lagi baru masuk ke Dashboard, kodenya mas :

<?php
set_time_limit(0);
error_reporting(0);
session_start();
require_once('mainconfig.php');
if($_SESSION['account'])
	die('Failed!');
if(!$_POST['username']||!$_POST['password']){
}else{
	header('Content-Type: application/json');
	$username = trim($_POST['username']);
	$cekuser = mysql_query("select * from members where username = '$username'");
	if(mysql_num_rows($cekuser)<1)
		die(json_encode(array('result' => 0, 'content' => 'Username/Password salah!')));
	$hasil=mysql_fetch_assoc($cekuser);
	if(trim($_POST['password'])<>$hasil['password'])
		die(json_encode(array('result' => 0, 'content' => 'Username/Password salah!')));
	$_SESSION['account'] = $hasil;
	print json_encode(array('result' => 1, 'content' => 'Login Berhasil!,anda akan dialihkan..', 'redirect' => '?'));
}

apa ada yang salah ? biar waktu submit langsung ngejalanin perintah ini

json_encode(array('result' => 1, 'content' => 'Login Berhasil!,anda akan dialihkan..', 'redirect' => '?'));