Squid continuously ask me the upstream proxy password…

[grzmrc]

Hi all,
my users surf internet by using a isa server 2006 proxy that is located in a remote site(my AD users are not in the same domain as isa server). I'd like to speed up the page downloads by installing squid3 on my pfsense 2.1.

After configuring the remote cache in squid, my users can surf pages correctly using squid proxy, but they are continuously prompted with a password request by squid IP.
in squid authentication I choiced "PASS". What I can do to get only one authentication prompt?
thanks