Hi,
I guess, this is happening because of cookies. Sometime back in read some
article on msdn or somewhere, about this, when I encounter this same error.

I dont know about Nokia Mobile Browser 4.0 but your code will work for few
browsers, but on some browser it will fail just because of those browsers
redirect the url without saving the cookie. And the original request is goes
back to the authentication cookie.

Solution
MMIT provides some solution for this senario that you can use
System.Web.Mobile.MobileFormsAuthentication class. This class is in
System.Web.Mobile namespace.

MobileFormsAuthentication.RedirectFromLoginPage(uName, false);

Check it out. I tried to search again but without success.

Try out.

Sachin Korgaonkar