Important! If you attempt to register and do not get an email within 5 minutes please check your spam box. This is especially true for Microsoft owned domains like Hotmail, Outlook, and Live. If these do not work please consider Gmail. Yahoo, or even AOL email which works fine.
It means they have chosen to be "Marked a s Invisible" - Most members would not see them listed. You can see them only because you are an Ultra-Premium member.