About adding external users

Hi, everyone. I have difficulty in adding new external users on Box and there two cases. The first: I can send invitation mail to new users and they can accept it, but can not see and use any folders on Box. The second: When I try to send invitation mail to users whose address include @me.com, Box says like this user is not NON active. I am not sure whether or not this trouble comes from their domain, because I could add external users whose address has @me.com. I need any assistance. Thank you Michimoto