Thank you for using our software and sincerely sorry for this issue. It is impossible to register the old kindle for pc currently. You can register this latest kindle for pc but disable the use of kindle kfx format by this way to remove kindle drm:
Thank you for using our software and sincerely sorry for this issue. It is impossible to register the old kindle for pc currently. You can register this latest kindle for pc but disable the use of kindle kfx format by this way to remove kindle drm: