I just got a tech support question from a site visitor who wants to register on our website. She said that it tells her her e-mail address is already in use, even though she has never registered on our site before.
I searched in our full user list and there is no one using her e-mail. But sure enough when I attempt to register with it, I too get the same error about it already being in use.

Any idea why it would do this and how to fix it?

Thanks,
Kari