добавьте следующий атрибут в раздел настроек членства в файле Web.Config.
requiresQuestionAndAnswer="false"
полный пример
<configuration>
<connectionStrings>
<add name="SqlServices"
connectionString="Data Source=MySqlServer;Integrated Security=SSPI;Initial
Catalog=aspnetdb;" />
</connectionStrings>
<system.web>
<membership
defaultProvider="SqlProvider"
userIsOnlineTimeWindow="20">
<providers>
<remove name="AspNetSqlProvider" />
<add name="SqlProvider"
type="System.Web.Security.SqlMembershipProvider"
connectionStringName="SqlServices"
enablePasswordRetrieval="false"
enablePasswordReset="true"
requiresQuestionAndAnswer="false"
passwordFormat="Hashed"
applicationName="/" />
</providers>
</membership>
</system.web>
</configuration>