Sorry everyone...this one was completely my fault.
I've been playing around with another idea I have for a cool site addition, and for that I needed an additional database installed. I did so last night, but the database password I used for it also got applied as the password for the existing databases, including the ones for the forum and the Photo Galleries. Since the new password in the database didn't jive with the password entered into the forum's and galleries configuration files, access would have been denied.
Not realizing the snafu, I messed around with that new database till about 1:30 AM and then went to bed, without checking back into the forums. When I got up this morning and went to log into the forums, I got that same error message, and I immediately knew what happened. I changed the passwords back so that all installed databases use the same password, and things were immediately back to normal.
I'll try to monitor things a little closer in the future when I working with these.