So we had a classic failure - classic because it affected me too, I was just as locked out as you all. Fortunately, the great guys at the hosting company were able to fix the database enough to let me in.
It happened about 2 am last night - and after that there were over 2,000 attempts to access the forum by 'guests' I guess these could be frustrated bots.
The post where it failed was from a 'content spammer' that traces to china form a computer that has had security issues, according to a brief look on the web. The good news is that we are still keeping them out, a little winged but no damage that I can find.
It does put more of a pressure on us to upgrade the software to the latest versions - obviously we are going to see more incidious attempts to hack the site and we could easily loose it. On those lines, I do periodic backups but some posts would inevitably be lost.