Not able to add new user, looks like the new user already has an account

I did the following: 

1. Invited a new user 

2. New user received a confirmation email

3. New user clicked on account settings on the email and nothing happened 

4. I removed the new user email and tried adding him again and it showed an error 

5. I cannot longer add any user with the same domain 

I need help here from box to add this new email into my account