Hi,
I don't know what you did for your migration, but if you were missing files, it's probable that some other things are messed up.
The best would be to install the latest version of HikaShop.
That will run some processes during the update process which might help clean some of the issues.
Regarding the error "you do not have access to the private section of this website", there is no such error in HikaShop.
This comes from Joomla and it happens because the current menu item has been configured to not be accessible by the user group of the current user.
So I would recommend to check the access level of your menu items and make sure that the settings of the Joomla user manager are correct (correct user group for new users, correct ACLs for that user group, etc).