Do some changes in createthumbnail function according to this link.
Instead of
$this->load->library('image_lib',$config);
use
$this->load->library('image_lib');
// Set your config up
$this->image_lib->initialize($config);
// Do your manipulation
$this->image_lib->clear();
New createThumbnail function:
//Create Thumbnail function
function _createThumbnail($filename)
{
$this->load->library('image_lib');
// Set your config up
$config['image_library'] = "gd2";
$config['source_image'] = "images/uploads/" .$filename;
$config['create_thumb'] = TRUE;
$config['maintain_ratio'] = TRUE;
$config['width'] = "80";
$config['height'] = "80";
$this->image_lib->initialize($config);
// Do your manipulation
if(!$this->image_lib->resize())
{
echo $this->image_lib->display_errors();
}
$this->image_lib->clear();
}