i have got this error on this part of code :

if (e.CurrentStepIndex == 0)
{
System.Web.UI.WebControls.Login l = (Login)Wizard1.FindControl("Login1");

if (Membership.ValidateUser(l.UserName, l.Password))
{
FormsAuthentication.SetAuthCookie(l.UserName, l.RememberMeSet);
e.Cancel = false;
}

Any Ideas?

found the solution
have a look here :
http://forums.asp.net/p/1374684/2887355.aspx#2887355