It's like the whole forumco server/site has gone down. I have seen this on a number of occasions as have members of another forum I use. See this post (which includes a response from forumco support):
This also happened briefly about 10 minutes ago. I was on the site an hour ago and it was fine but my wife tried 10 mins ago from a different PC and it was not found and I got the same on my PC when I tried. Then a few minutes later it started working again.
I think there may be some other problem. You mention a firewall problem that was fixed quickly but since I joined the halfdozen forum last November I have seen 3 outages. Two of them were for more than an hour and one seemed to last half a day (ish).
Since setting up the ding forum last week I have seen it down on 4 occasions - 3 were just a few minutes but once it was for more than an hour (Last Saturday - 14th Jan).
Two of my other members notices Saturday's problem too so that would seem to rule out my PC.
Don't get me wrong. I'm not having a go at you or at forumco. I think the free forums are cool (and excellent value!)