CreateUserWizard怎么获取定制控件

CreateUserWizard如何获取定制控件？
DropDownList   RoleSelect   =   (DropDownList)CreateUserWizard1.CreateUserStep.FindControl( "Role ");
报未将对象的引用设置到对象的实例

------解决方案--------------------------------------------------------
DropDownList RoleSelect = (DropDownList)CreateUserWizard1.CreateUserStep.ContentTemplateContainer.FindControl( "Role ");