public function addPerson(){
  $username = $this->input->post('username');
  $password = $this->input->post('password');
  $accesslevel = $this->input->post('accesslevel');

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

      //are you trying to put it in the view? or this is your model?
      $this->template->show('Admin', $this->TPL);
    }
    if(strlen($data['myerror']) != 0){
      //This line may caused your error, what is this line for?
      $this->TPL["myError"] = $myerror;

      $this->getAllPerson();
      $this->template->show('Admin', $this->TPL);
    }
}