Die Funktion Validate() im Login Button Click Event war das Problem für das nicht validieren Methodik um einen Anonymen (gesichts- / namenslosen Accounts / Zugriff) auf der Seite zu gewähren.

Web.config

@@ -27,7 +27,7 @@
     <authentication mode="Forms">
       <forms defaultUrl="/Customers/CustomsAviso.aspx" loginUrl="login/Login_FLEX.aspx" slidingExpiration="true" timeout="2880"/>
     </authentication>
-    <sessionState mode="InProc" timeout="2880" cookieless="UseCookies" regenerateExpiredSessionId="true" compressionEnabled="false"/>
+    <sessionState mode="InProc" timeout="2880" cookieless="false"  regenerateExpiredSessionId="true" compressionEnabled="false"/>
     <httpRuntime requestValidationMode="2.0" targetFramework="4.7"/>
     <pages validateRequest="false" controlRenderingCompatibilityVersion="4.0"/>
     <!--<securityPolicy>

login/login_FLEX.aspx.vb

@@ -46,7 +46,9 @@ Partial Class login_login_TEST
                             CustomerIDTextBox = Login1.FindControl("CustomerID")
                             Session.Add("CustomerID", CustomerIDTextBox.Text)
                             Session.Add("PW", Login1.Password)
-                            FormsAuthentication.RedirectFromLoginPage(User.Identity.Name, True)
+
+                            FormsAuthentication.RedirectFromLoginPage(Login1.UserName, True)
+
                             'FormsAuthentication.SetAuthCookie(Login1.UserName, True)
                             'Response.Redirect("../Customers/CustomsAviso.aspx")
                             Exit Select
@@ -59,7 +61,7 @@ Partial Class login_login_TEST
     End Sub
 
     Protected Sub LoginButton_Click(sender As Object, e As EventArgs)
-
+        Validate()
     End Sub
 
     Protected Sub CustomerID_TextChanged(sender As Object, e As EventArgs)