It might be happening because the address that has been mapped to the order is being deleted from the system. You can try debugging the issue after enabling error degugging.
FYI, to enable error debugging you can follow the steps below.
- open file: config/defines.inc.php (using FTP or hosting control panel)
- change false-->true:
define('_PS_MODE_DEV_', false);
define('_PS_MODE_DEV_', true);