missing users

I added some people to my user list but they never received a login email, so I deleted them. Then I added them in again. Their name shows up on the list but they never received a login message. When I try to do "forgot password" with their email address, it says the user is missing.

When I go into the user list and delete them, they receive an email saying that they have been removed from the list. But they never get any login screen.

Please help!!!