I just got a MySQL error trying to log in from Firefox (just installed so it's definitely the latest version) and I know I typed the wrong password, but that notification popped up instead of the wrong password screen. I checked Subeta on Chrome and everything was fine, so I'm not sure what's going on, but I figured I'd report it anyway in case something was up. I know literally nothing about MySQL so I don't really know what else would be relevant.
Edit: Missed that there was already a topic on my issue. ^^;
I'm having a different issue with logging in, but they might be related so I'll post this here. Seems there's something screwy with the login in general. :/
When I came to Subeta's main page I saw a "Welcome back" and "Continue to Subeta!" message instead of the login box. I tried clicking the "Continue" link, which took me to the same MySQL error you got. Refreshing showed me the news page, but I wasn't logged in.
Returning to the home page didn't help. Same "Welcome back" message. Got the MySQL error again when I tried to continue. I also tried using the logout link, but it still behaved like I was returning to an already logged in account. In the end I was able to find a login page through Google.
This is happening in both Firefox and Chrome.