CodeIgniter验证错误

I am trying to use CodeIgniters built in validation to validate my form however whenever I add

<?php echo validation_errors(); ?>

My html code breaks and nothing beyond this point comes up on the website, and my page source just closes off tags and thats all.

Heres my form code:

<html>
<body>

<?php echo validation_errors(); ?>

<form action="myController/validate" method="post">

Username<input type="text" name="username" value="" size="50" />

</form>

</body>
</html>

And my php code:

public function validation() {
    $this->load->library('form_validation'); //load the library for validation

    $this->form_validation->set_rules('username', 'Username', 'required'); // set rules, u can make it more complex

    if ($this->form_validation->run() == FALSE) {
        $this->load->view('loginView'); //redirect to registe.php if there is any error
    } else {
        $data['msg'] = 'Your details been registered successfully';
        $this->load->view('login', $data); //if there is no error redirect to login.php with success message
    }
}

Does anyone know why this could be the error?

Found the answer, I hadn't loaded it up on the autoload. If anyone else has the same issue, go to the autoload.php file and in your libraries add 'form_validation'.