Problems with adding users.

I use my WordPress as a classroom tool in a college writing course. I am having trouble adding two users. Both have registered with WordPress accounts and neither can access the blog itself when they log in. One has accepted the invitation and registered, but from my end it shows that the invitation status is still classified as “waiting.” What can I do to help them? Thanks in advance for any help you can provide, since this is a summer course we need help ASAP.

ACW