Hi @amirhosein
I think you do not need to add that property to the DB table users - it could be saved in the DB table user_settings. For that you would need to add it also in the UsersDAO function getAdditionalFieldNames (https://github.com/pkp/pkp-lib/blob/master/classes/user/PKPUserDAO.inc.php#L464). In that case you would set the user metadata in the RegistrationForm something like this: $user->setData('sex', $this->getData('Sex'));
Else, if you want to use the new DB column, you would also need to add the getSex and setSex to the classes/users/Users.inc.php bzw. PKPUser.inc.php class and also consider it everywhere in the UsersDAO.inc.php i.e. PKPUsersDAO.inc.php. Thus the solution above needs less code change.
When you see a white page, it means that an error occurred. You can then take a look in the apache/server error log files to see what error occurred.
Best,
Bozana