How to debug SQL queries when you stuck
Print you query and run it directly in mysql or phpMyAdmin
$date = "2012-08-06";
$query= "INSERT INTO data_table (title, date_of_event)
VALUES('". $_POST['post_title'] ."',
'". $date ."')";
echo $query;
mysql_query($query) or die(mysql_error());
that way you can make sure that the problem is not in your PHP-script, but in your SQL-query
How to submit questions on SQ-queries
Make sure that you provided enough closure