Sounds like 2 things going on here...

1. Brute force attack.
Likely rotating usernames with the passwords in an attempt to keep from getting locked out, but obviously running into dupes too quickly (causing the temporary lockouts).

2. Social engineering(?)
The guy I got the same lame private message from called himself "einstein2".
I'm not sure if there might be something embedded in the message (I didn't bother reading through the HTML), but it did include a link to http://stein.freehostia.com (which is blocked by our proxy). I would not recommend following the link, as it may host malware.