can't get "setAuthCookie" to persist a cookie

I have a login control with a checkbox called "rememberMe".  In the Login1.LoggedIn event, it checks the value of this checkbox, and if its true, it does the following:                  
currentuser = Membership.GetUser(Login1.UserName) username = currentuser.UserName FormsAuthentication.SetAuthCookie(username, True) This is supposed to make the browser remember the user so that he does not have to log on every time he visits the site.
It does not work.  I stepped through it with the debugger, and the username is correct, and the "setAuthCookie" is indeed set. 
When I start my browser a second time, I check in the global.asax session_start event whether User.Identity.IsAuthenticated is true, and it isn't.  I would think it would be, if ...