Edit: Fixed for now. (Downgraded to a php version that worked. Everything will have to be upgraded again at a later date.)
Dreamhost ‘upgraded’ the phpbb on my domains today, which broke the Almeopedia and, even more annoyingly, the ZBB.
The symptom: logins don’t work. They give some cryptic messages, and you get a success message, but when you return to the main page you are not actually logged in.
If you’re already logged in, it seems to work OK, so don’t log out. If you’re logged out, you’re out of luck, for now.
I’ve complained to Dreamhost, so hopefully they will fix things tomorrow.