.NET FormsAuthentication issue with load balanced servers using IIS 7 and using cookies

I have a couple of load-balanced web servers running .NET 3.5 / MVC 2 application. We use cookie authentication.

When the user starts on the second server, he HttpContext.Current.User.Identity.IsAuthenticatedalways returns as false, and therefore the user logs off.

Another interesting tidbit is that the cookie .ASPXAUTHis still being sent from the browser, can still be seen in the request headers, but no longer exists in HttpContext.Current.Request.Cookies. I set auth cookie HttpOnlyand Securein true.

I verified that both web servers use the same exact machine keys as those in the web.config files.