When registration/login is enabled on the GiveWP installation, and a donor already has an account on the installation, she/he can only make a donation by logging in first. If the email address of the account is provided and the donor is NOT logged in, an error is shown.

Ideally, people, also registered donors, should be able to make a new donation without having to log in, just as is possible with email access / users without registered accounts. This error that is shown for registered users may cause them to leave the donation process if they do not have their password handy, for example.