Server 500 Error After Read $_POST on API - php

Question

i'm still build an API for android app. I follow this tutorial: http://www.androidhive.info/2012/01/android-login-and-registration-with-php-mysql-and-sqlite/.
When I try to submit: It will be SERVER 500 ERROR.
Check the demo:
FORM: http://simedik.masterbiz.net/api/form.php
<form action="login.php" method="post">
<input type="text" name="email"/>
<input type="text" name="password"/>
<input type="submit" value="SUBMIT"/>
</form>
Anyone have solution for this? Thanks in advance!
LOGIN.PHP SCRIPT
<?php
require_once 'DB_Functions.php';
$db = new DB_Functions();
// json response array
$response = array("error" => FALSE);
if (isset($_POST['email']) && isset($_POST['password'])) {
// receiving the post params
$email = $_POST['email'];
$password = $_POST['password'];
// get the user by email and password
$user = $db->getUserByEmailAndPassword($email, $password);
if ($user != false) {
// use is found
$response["error"] = FALSE;
$response["uid"] = $user["unique_id"];
$response["user"]["name"] = $user["name"];
$response["user"]["email"] = $user["email"];
$response["user"]["created_at"] = $user["created_at"];
$response["user"]["updated_at"] = $user["updated_at"];
echo json_encode($response);
} else {
// user is not found with the credentials
$response["error"] = TRUE;
$response["error_msg"] = "Login credentials are wrong. Please try again!";
echo json_encode($response);
}
} else {
// required post params is missing
$response["error"] = TRUE;
$response["error_msg"] = "Required parameters email or password is missing!";
echo json_encode($response);
}
?>
DB_FUNCTIONS.PHP
<?php
class DB_Functions {
private $conn;
// constructor
function __construct() {
require_once 'DB_Connect.php';
// connecting to database
$db = new Db_Connect();
$this->conn = $db->connect();
}
// destructor
function __destruct() {
}
/**
* Storing new user
* returns user details
*/
public function storeUser($name, $email, $password) {
$uuid = uniqid('', true);
$hash = $this->hashSSHA($password);
$encrypted_password = $hash["encrypted"]; // encrypted password
$salt = $hash["salt"]; // salt
$stmt = $this->conn->prepare("INSERT INTO users(unique_id, name, email, encrypted_password, salt, created_at) VALUES(?, ?, ?, ?, ?, NOW())");
$stmt->bind_param("sssss", $uuid, $name, $email, $encrypted_password, $salt);
$result = $stmt->execute();
$stmt->close();
// check for successful store
if ($result) {
$stmt = $this->conn->prepare("SELECT * FROM users WHERE email = ?");
$stmt->bind_param("s", $email);
$stmt->execute();
$user = $stmt->get_result()->fetch_assoc();
$stmt->close();
return $user;
} else {
return false;
}
}
/**
* Get user by email and password
*/
public function getUserByEmailAndPassword($email, $password) {
$stmt = $this->conn->prepare("SELECT * FROM pasien WHERE kd_pasien = ?");
$stmt->bind_param("s", $email);
if ($stmt->execute()) {
$user = $stmt->get_result()->fetch_assoc();
$stmt->close();
return $user;
} else {
return NULL;
}
}
/**
* Check user is existed or not
*/
public function isUserExisted($email) {
$stmt = $this->conn->prepare("SELECT email from users WHERE email = ?");
$stmt->bind_param("s", $email);
$stmt->execute();
$stmt->store_result();
if ($stmt->num_rows > 0) {
// user existed
$stmt->close();
return true;
} else {
// user not existed
$stmt->close();
return false;
}
}
/**
* Encrypting password
* #param password
* returns salt and encrypted password
*/
public function hashSSHA($password) {
$salt = sha1(rand());
$salt = substr($salt, 0, 10);
$encrypted = base64_encode(sha1($password . $salt, true) . $salt);
$hash = array("salt" => $salt, "encrypted" => $encrypted);
return $hash;
}
/**
* Decrypting password
* #param salt, password
* returns hash string
*/
public function checkhashSSHA($salt, $password) {
$hash = base64_encode(sha1($password . $salt, true) . $salt);
return $hash;
}
}
?>