You are most likely running MySQL in strict mode, but it could also be a bug in your MySQL version. MySQL strict mode issues have been fixed in TYPOlight version 2.5.0, so either update your TYPOlight installation or check out the two related bug reports below:
http://bugs.mysql.com/bug.php?id=19498
http://bugs.mysql.com/bug.php?id=14786
Last update on 2008-08-04 by Leo Feyer.