Why can't I access webpages I have visited recently when I am offline?

My IE6 does maintain a "History" list, but the entries are greyed-out
when I go offline, and anything I click on tells me "This page is not
available offline".

This problem also affects my Homepage, and even pages I have set as
"Make available offline" and synchronised as instructed by IE6.

I assume that there is conflict between IE6 and another program (I am
running Norton Anti-Virus 2003 (with current updates) or Norton
Personal Firewall 2004), but I cannot see any obvious setting to
change.

My operating system is Windows XP Professional with SP1 and SP2, and
the problem has arisen since I installed SP2, though I do not think it
happened immediately.  I find that there are pages
in my Favourites list which I have not accessed online since this
problem started, and these are not greyed out and do remain available offline.

Many thanks

well, if the page requires authentication it cannot be accessed in
your history i.e you cannot view your emails etc

It's not just pages requiring authentication, it won't allow me to
access ANY page I have visited, even though the page is clearly listed
in History (but in grey - gray in US? - when I'm offline)