Upload problem in CodeIgniter

I am getting this error:

The upload destination folder does not appear to be writable.

But is_dir and is_writable both return true.

$config['upload_path'] = './work_order_doc/';
$config['allowed_types'] = 'gif|jpg|png';
$config['max_size']= '100';
$config['max_width']  = '1024';
$config['max_hei开发者_JAVA技巧ght']  = '768';
$this->load->library('upload', $config);
$work_order_file="work_order_file";

var_dump(is_dir($config['upload_path']));
var_dump(is_writable($config['upload_path']));



if ( ! $this->upload->do_upload($work_order_file))
   {
     $error = array('error' => $this->upload->display_errors());
     print_r($error);
     $temp="";
     }
else
 {
   $upload_data = $this->upload->data();
   echo $temp=$upload_data['file_name'];
}

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Maybe your host have blocked file uploads? You can always try to specify full path to the upload directory.

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Your PHP configuration may be not allowing you to get to the file/directory, try checking open_basedir in php.ini and make sure it is in allowed paths.