Had it a couple of times today, once when trying to read this thread, and I've had it once before, last week. It seems that it is a server issue, but I'm not sure whether that would be the host server or the web server.
You have to clear the browser cookies and cache, Justin. I've not got round to doing it on this computer but I did the one at work and phone and now it works.
When I access the forum, I see &sid=0123456789abcdef0123456789abcdef (or whatever my session ID is) in the URL. I don't think that was the case with the old domain. I would have thought that the session ID would be stored in a cookie and not as part of the URL.
"We are the Queen's shield. We are the nation's shield." —Sir Nicholas Fury, 1602