I know on my board, when someone is trying to post Asian characters, they will get a similar error. Can't recall if it is the exact, but you could check with this user if they are trying to post anything 'odd'.
It could be that they are trying to post a character that other users are not and that is the reason only they experience it. You should try the "The Fix" in this article Doesn't have a default value errors or the MySQL Upgrader tool in the Support Toolkit and see if that resolves the error.
It's not a problem with 3.0.12, the issue is caused by the utf8 character set used by MySQL DBMS not supporting 4 byte characters that are outside the MBP (Basic Multilingual Plane). MySQL has added another character set, utf8mb4, but it is only available on MySQL 5.5.3+, which not many web hosts run.