Yes, well... my fault.
We have a "persistant pest" who has a script running against the site that tries to hack in every 3-5 minutes. I turned on some new security features to block it and as a result, ended up blocking some users too.
I'm trying to learn more about what this guy is doing, and how I can block him, but it's going to take some time, as I'm not really security "savy". Any internet security gurus out there?
For now, just make sure your passwords are good (6 or more characters, mixture of upper and lower case, use at least one number and one "special character" like !, %, & etc.