QuestionAndAnswerRequired property of createUser Wizard

Question

Hello,
I have a createUserWizard and want to set the QuestionAndAnswerRequired property to false but I get an error:
Message 1 Validation (ASP.Net): Attribute 'QuestionAndAnswerRequired' is not a valid attribute of element 'CreateUserWizard'.
<asp:CreateUserWizard ID="CreateUserWizard1" runat="server"
MembershipProvider="SPS_MembershipProvider"
RequireEmail="False" QuestionAndAnswerRequired ="false"
ConfirmPasswordLabelText="confirm password" PasswordLabelText="password"
UserNameLabelText="Email" >
why is that and what can I do?
Thanx for your kind help .