Netasq F25 - Proxy Authentication stop working... !!!! Help please.

First of all, excuse for my orrible english !

I buyed the F25 netasq firewall with 6.2.4 firmware and Kappersky AV
4.0.1.
With a basic configuration, made by the seller, the firewall ask for
authentication on http request.

Afterwards, I updated the appliance with the new firmware 6.3.1.1 and
with the new av engine 4.0.2.
After the restart, the automatic redirection to proxy authentication
stop to work.
Opening the browser, after few seconds, appear the "Page not found".

However, the authentication service it's ok.

In fact, calling manually the ip address of the firewall, the
authentication portal appear regularly permitting the user
authentication.

After the logon, it's possible browse web without problem.
In the same way, making the logout, surfing web is denied.

I tried thousands of experiments without results.

Could you help me to understand the issue ??

Is there any simple "How to..." to understand the authentication
configuration ?

Thanks to everyone wants to help me.

Bye