Problem with user login validation by authlogic

Question

Hi, I want to use email for signing in, and to allow users to have similar names. One way to do this is to rename login/username field to something different. However, I would prefer to do it just by authlogic settings. I tried the following

acts_as_authentic do |c|
    c.login_field :email
    c.validate_login_field false 
    c.validate_email_field true
end

but it still complains that the login already exists. What must be done to avoid username validation without renaming the field? .