Forms Authentication Fails some times and not some times???

[Guest]

Hi,

I am running into this wierd problem. After validating the user I set the
authentication cookie
FormsAuthentication.SetAuthCookie(userName, false);
HttpContext.Current.Response.Redirect("Default.aspx?somevar=" + someVar);

in Default.aspx I check if the user is authenticated.
This works some times and some times it does not work.

I checked the IIS logs and I see two entries for Default.aspx in the failed
sessions.
In the second entry in IIS log I would see that its missing the
authentication cookie.

I don't understand whats going on.

Any help...??????