Yes, I too have suddenly experienced exclusion from a regularly-visited website (and, indeed the whole family of URLs constituting the 'parentage' of that website).
AFAIK I've not downloaded or installed any changes that might affect my Firewall(s). I'm with Virgin Net Broadband and operate through a Netgear DG834G Wireless Router (with whatever inbuilt security that entails) as well as Windows XP Home (Firewall enabled) and AVG 7.5 (paid for). I've tried with the AVG Firewall disabled (but not the XP one yet), but I cannot see how/why any of these firewalls would exclude a specific domain. I'm liberal and without children, so I don't have any nanny-software installed. AFAICT all other domains are available to me. I generally use Firefox, but I've tried Mozilla and Internet Destroyer (!) with identical results, viz:-
"The connection was reset
The connection to the server was reset while the page was loading.
* The site could be temporarily unavailable or too busy. Try again in a few moments.
* If you are unable to load any pages, check your computer's network connection.
* If your computer or network is protected by a firewall or proxy, make sure that Firefox is permitted to access the Web."
I've tried pinging and do get a response (though it disappears very quickly and all I get to see is bytes=32, time=345ms, TTL=49 then the DOS frame disappears after three tries.
Others that visit the 'suspect' website report no problems, and these other punters are located across the World (including the UK).
I'm totally at a loss as to what might be preventing me accessing this site (and, No, it's not porn!).