Class 'CI_Formgenerator' not found in C:\Users\mycode\system\core\C

I have the following code which produces a registration form. It works fine on the page load but on POSTing it tells me that CI_formgenerator cannot be found - even though I've clearly not called the function that. What am I doing wrong?

Code:

    public function index(){
        $this->benchmark->mark('code_start');
        
                $this->load->library('formgenerator',array('register'));

                $this->formgenerator->setupValidation();                        
                
                if ($this->form_validation->run() == FALSE){                                                
                        if (count($_POST)){
                                $this->formgenerator->populateForm($_POST);
                        } else {
                                $sample_data = array();
                                
                                $this->formgenerator->populateForm($sample_data);
                        }
                        
                        $form_out = $this->formgenerator->generateForm();
                        
                        $this->benchmark->mark('code_end');
                        $this->benchmark->elapsed_time('code_start', 'code_end').'<br>';
                        
                        $this->CI->autocontent['form'] = '<ul>'.implode($form_out).'</ul>'; // Autocontent can be an array of variables!
                } else {
                        $this->load->library('formgenerator',array('register'));
                        
                        $this->load->model('register');
                        
                        $this->register->saveUser($_POST);

                        echo 'Your registration has been successful. Please confirm your account in your email';
                }                                                                                
    }

The full error I get is:


A PHP Error was encountered

Severity: Error

Message: Class 'CI_Formgenerator' not found

Filename: core/Common.php

Line Number: 196

Backtrace:

{With no backtrace available}