[squid-users] [Squid] Invalid Response Error

When i browse this page:
http://www.regione.toscana.it/lavoroeformazione/pariopportunita/index.html
return me Invalid Response
I have Squid 3.0.25, PIX and Websense.
The structure is:
client-->Proxy-->PIX--(filter url)-->Websense

The strange is that i do refresh(F5) the page load correctly. What's
the problem?
All this with IE7 and IE8, i mustn't change the browser.

Thanks,
Jacopo

-- 
Linux, Windows Xp ed MS-DOS
(anche conosciuti come il Bello, il Brutto ed il Cattivo).
-- Matt Welsh