Codeigniter: Unable to locate the specified class: Exceptions.php - codeigniter

Question

Here's my controller:
$html = $this->load->view('print_po', $po, TRUE);
$this->load->library('pdf');
$pdf = $this->pdf->load();
Now I've tried and comment each line and the one that shows the error is:
$pdf = $this->pdf->load();
Here's my library class in application/libraries:
<?php if (!defined('BASEPATH')) exit('No direct script access allowed');
class pdf {
function pdf()
{
$CI = & get_instance();
log_message('Debug', 'mPDF class is loaded.');
}
function load($param=NULL)
{
include_once APPPATH.'/third_party/mpdf/mpdf.php';
if ($params == NULL)
{
$param = '"en-GB-x","A4","","",10,10,10,10,6,3';
}
return new mPDF($param);
}
}
The error comes only after moving the code from one server to another(the error happens on a CentOS server which I bet is case sensitive). My question here would be: what should I modify so codeIgniter loads Exceptions.php normally?

Answer 1

First, remove the forward-slash at the first of /third_party phrase:
include_once APPPATH.'third_party/mpdf/mpdf.php';
CodeIgniter defines APPPATH constant with a trailing slash. Take a look at index.php:
define('APPPATH', $application_folder.'/');
Second, make sure that the file/folder names are as the same as you have wrote. It's better to keep them all lowercase. Here is a related topic.
Update:
The class name should be Capitalized. In this case change the pdf to Pdf:
class Pdf {
// ...
}
From CI Documentation:
Naming Conventions:
File names must be capitalized. For example: Myclass.php
Class declarations must be capitalized. For example: class Myclass
Class names and file names must match.