That's because you don't have a file called /includes/languages/english/modules/shipping/old_usps.php on your site, however you do have one called /includes/languages/english/modules/shipping/usps.php which is possibly the one it's looking for.

Not sure where the old_usps.php has come from. If it's not something that you've changed that can be reversed then try uninstalling then reinstalling from scratch again and check any readme files that come with the mod in case there's specific instructions for it.

__________________
Lawrence