On standard Codeigniter installation, when your try to upload DMG (apple diskimage) file via Upload class of Codeigniter your may get error message like “The filetype you are attempting to upload is not allowed.”.
To fix such error add such line on PATH_TO_SITE/application/config/mimes.php
‘dmg' => array('application/x-apple-diskimage’, 'application/octet-stream’),
This line add proper MIME type for allowing upload apple diskimage application.