User registration locks admin out

Hi,

Recently the “submit” button on the login form disappeared. In an attempt to find a way to allow login, I checked “prevent core login”.
Now, User Registration prevents admin login, the only way through was to uninstall. After re-installing, the problem came back even though “prevent core login” was unchecked.

Is there a known bug about the submit button on the login form? Is there a way to re-install without locking the admins out?

thanks