Account locked: You have been logging in too frequently. Wait a few minutes before trying to connect again. Logging into the Yahoo! website may help.
Received invalid data.After all these messages, it simply connected by itself. I thought that it was a problem with the way Pidgin was authenticating on Yahoo!'s servers, but in the after-noon, I tried to login from a Window-based laptop, on Yahoo! Messenger 10, and surprise. It said that my password was wrong. OK, I gave it another try. And then another one. And I continued like this five more times.
In an end, I got an error which said that the messenger can't communicate normally to its servers (actually, my password wasn't wrong). After I got this, I successfully logged in at the following try.
I have no idea which is the problem, but I hope that Pidgin was wrong. I mean, I don't login frequently on Yahoo! and, anyway, I think that it was referring that somebody tries again and again to login from my account so it was locked because of this (exactly, I'm afraid that somebody tries to hack it).
If you have this problem please don't hesitate to leave a comment telling us also when your problem started!