form authentication - how to clear session with formsauthenication.signout - asp.net

Question

i have
<system.webServer>
<modules>
<add name="FormsAuthenticationModule" type="System.Web.Security.FormsAuthenticationModule" />
<remove name="UrlAuthorization" />
<add name="UrlAuthorization" type="System.Web.Security.UrlAuthorizationModule" />
<remove name="DefaultAuthentication" />
<add name="DefaultAuthentication" type="System.Web.Security.DefaultAuthenticationModule" />
</modules>
</system.webServer>
<authentication mode="Forms">
<forms loginUrl="Login.aspx" name=".TEST" timeout="15">
</forms>
</authentication>
<authorization>
<deny users="?"/>
</authorization>
<location path="images">
<system.web>
<authorization>
<deny users ="?" />
</authorization>
</system.web>
and in this images folder i have a web.config with
<?xml version="1.0"?>
<configuration>
<system.web>
<authorization>
<deny users="?"/>
</authorization>
</system.web>
</configuration>
in IIS authentication is set to Form Authentication and Annoynomous so user can get to login page.
It is working correctly if you haven't logged in and try to browse the images folder. Once you are logged in, it let you browse to that images folder. However when you are logged out, it doesn't delete the session and still let you browse the images folder. The code below should have killed all sessions but it apparently doens't do so. Please let me know if i miss something. Thank you
FormsAuthentication.SignOut()
Session.RemoveAll()
Session.Abandon()
For Each key As String In Request.Cookies.AllKeys
Dim cookie As New HttpCookie(key)
cookie.Expires = DateTime.UtcNow.AddDays(-7)
Response.Cookies.Add(cookie)
Next
FormsAuthentication.RedirectToLoginPage()