Database Error!

Error: Field 'last_seen' doesn't have a default value
Query: INSERT INTO users (uid, password, ip_address, first_seen) VALUES ("5cea33d4733800.55614619", "Xm6Hwa3S3qwZpT0DiPFrYxjQ9lyJzBcO", "54.227.76.35", UNIX_TIMESTAMP())
File: /includes/database.class.php
Line: 98
Backtrace: