I've gotten that message here recently with IE and FF.I got the message trying to access this thread in Googe Chrome:
http://www.longhaircareforum.com/entertainment-celebrity-news-more/505345-colored-girls-screening.html#post12149305
I was able to access the same thread using IE which I also have on my computer. It is a message from NGiNX that says, "Page not available. Contact the administrator." I also get it while I'm already viewing a thread. If I click from page "1" (which I was able to view) to page "2" I get the error message.
IE is the only browser allowed at work unfortunately so I'm unsure if this DNS issue would hold true for other browsers. Perhaps it is my work's network but why would that all of sudden become an issue? Know you can't answer this since it appears to be my work's network that's experiencing difficulties but it's just ironic how the series of events are playing out. As for IE's cache, thank you, noted.Can you access the site from work with anything other than IE? If no again then it is your work network.
I have found that IE has some weird cache that renews itself whenever it wants to. The site is no longer slow. I run tests on it and the start to finish on a page is on average 6.5 seconds. The content itself is between 1.5-2 seconds.
What link are you using? The old links we had for the forum had the /forum/ in the URL whereas we don't have that any more.
Can you access the site using IE and just typing the address in your browser's address bar?