I'm having problem with our login procedure.

Some customers complain that they can't login. I can see in our logs that their login is successful and that they are redirected from the login page to the member area. But there somehow the login isn't detected and they are bounced back to the login page.

I've asked customers to check if cookies are supported (http://www.html-kit.com/tools/cookietester/) but problem remains even if this test returns true.

This is how I've implemented the login procedure (simplyfied):

protected void Login(string email, string password)
{

FormsAuthentication.SignOut();


Guid clientId = /* Validate login by checking email and password, if fails display error otherwise get client id */


FormsAuthentication.SetAuthCookie(clientId.ToString(), true);

HttpContext.Current.Response.Redirect("~/Members.aspx");


}

On the member page I check for authentication by in Page_Load function:

public static void IsAuthenticated()
{
 if (!HttpContext.Current.User.Identity.IsAuthenticated)
 {
         HttpContext.Current.Response.Redirect("~/Login.aspx", true);
 }
}

Maybe I'm using FormsAuthentication completely wrong?

I've asked this before but still haven't been able to figure this out, I'd appreciate any help.