"A PHP Error was encountered Severity: Notice Message: Undefined variable: " in Codeigniter

Question

I am getting a notice in code igniter and am not sure of how to get rid of it. I have an admin.php view file with the following relevant code:

Admin page

<p><strong><div id="myErr">
<?php  
echo "$myError";
?>
</div>
</strong></p>

I have an Admin.php control file with the following relevant code:

public function addPerson()
{
  // GET AND SET POSTED DATA
  $username = $this->input->post('username');
  $password = $this->input->post('password');
  $accesslevel = $this->input->post('accesslevel');
  $myerror = "";
  // add the person to database with

    if (strlen($username) < 1)
    {
      $myerror = "The Username field is required.";
    }
    if(strlen($myerror)==0)
    {
      $this->db->query("INSERT INTO usersas6 "."(compid,username,password,accesslevel) VALUES "."(null,'$username', '$password', '$accesslevel')");
      $this->getAllPerson();
      $this->template->show('Admin', $this->TPL);
    }
    if(strlen($myerror) != 0){
      $this->TPL["myError"] = $myerror;
      $this->getAllPerson();
      $this->template->show('Admin', $this->TPL);
    }
}

The setup actually works when I submit the relevant form. The error output appears! But there is this warning message on the loaded page (prior to submitting the form) and I am not sure how to get rid of it.