Forum Users Get Message Saying They Already Have an Account
 

I've suddenly started experiencing a new issue today.

I have new users that are trying to sign up for my 4.0 forum. When they go though the sign up screen, they are told that their user name already exists. However, when I check the user list, no such user has signed up. This has happened with two new users today, and I've had to manually set them up as users.

What gives?