Call to undefined method VI_Loader::_ci_load_class()

I am try to update a site from CodeIgnitor 2.2.2 to 3.1.6

I am getting

A PHP Error was encountered
Severity: Warning
Message: Declaration of MX_Loader::helper($helper) should be compatible with CI_Loader::helper($helpers = Array)
Filename: MX/Loader.php
Line Number: 389
A PHP Error was encountered
Severity: Warning
Message: Declaration of MX_Loader::helpers($helpers) should be compatible with CI_Loader::helpers($helpers = Array)
Filename: MX/Loader.php
Line Number: 0
A PHP Error was encountered
Severity: Warning
Message: Declaration of MX_Loader::_ci_get_component($component) should be compatible with & CI_Loader::_ci_get_component($component)
Filename: MX/Loader.php
Line Number: 0
A PHP Error was encountered
Severity: Notice
Message: Only variables should be assigned by reference
Filename: core/Loader.php
Line Number: 784
A PHP Error was encountered
Severity: Notice
Message: Only variables should be passed by reference
Filename: MX/Loader.php
Line Number: 135
An uncaught Exception was encountered
Type: Error
Message: Call to undefined method VI_Loader::_ci_load_class()
Filename: /home/zqnoinxl/cherylibarra.burtonconstruction.net/application/libraries/MX/Loader.php
Line Number: 152

Line 152 is

$this->_ci_load_class($library, $params, $object_name);

VI_Loader is under the core library

cand start with

<?php (defined('BASEPATH')) OR exit('No direct script access allowed');

/* load the MX_Loader class */
require APPPATH."libraries/MX/Loader.php";

class VI_Loader extends MX_Loader {

Why can't it find it? Any ideas please

Best regards

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