My first thought would be that they have entered an invalid email address.
Yes…and it is my first thought that as well, except I myself have had the same error in the past when creating a user. So, I wonder if there might be some other bug at play. (For the most recent person reporting the error, I also double checked that they were not already registered using that email address.)
While we’re at it, any idea why sometimes users don’t have a clickable area or a fill-in field when they receive an email to change their password. (I have experienced this as well, once – I had to use my Admin login and change the password manually, which is what I end up doing for the users who have this same problem. I should note, It’s rare. I have about 30 new users per day, but only once a month or two does someone report this error.)
So, the only reason you would get this error from TML/WP core is if the email already exists or they didn’t actually enter an email address. I can’t speak for any other plugin you may have enabled.
Can you elaborate on your second question? I don’t follow.
