2nd admin Can't login

I have a need to have 2 admins in my blog. The second admin user was created and both myself and him were able to login as the second admin user.

However the next day, the 2nd admin can no longer login. So I delete him as a user, create a new admin user, and login in as that user with no problems. However, the 2nd admin user can still not login. Any ideas?