After several phone calls to our host I've learned that last night they moved the forum from one of their old servers to a new one. However, in the process somehow they managed to lose parts of the forum's database and without those parts the forum will not run correctly, which is why everyone has been getting a fatal error when they try to visit.
Now, beyond that, there's good and bad news. The good news is that I make backups of the database at least once a month. The bad news is the last time I did one was August 24th, which means 18 days worth of posts are likely to be gone without the ability to recapture them in the form they were in, all thanks to whatever happened when our host moved us. Perhaps they'll show up somewhere from the ether, but let's not count on it. Though it could be much worse - all our posts would be gone forever if it wasn't for my backup. So, just 18 days of posts gone is but a very small fraction of more than 15 year's worth of posts.
I'll be working on restoring all the old stuff, but first I'm just going to restore some of the latest posts up to August 24th just so that we can get the forum back up and running. And hopefully I can get that done as quickly as possible...
UPDATE: A new version of the forum is finally up and running. However, only Midnite and I have access to it at the moment because we're making sure things are running as smoothly as possible without all topics/posts available as yet. Look for it to be available to all sometime Wednesday!
SECOND UPDATE: The new (and only temporarily looking like it does) version of the forum is up and running smoothly (so far as we can tell) and available to all. To access it use this URL: http://www.dsboards.com/SMF/index.php - and you will likely need to log in.