Database Error!

Error: Field 'last_seen' doesn't have a default value
Query: INSERT INTO users (uid, password, ip_address, first_seen) VALUES ("5c6a0725320f93.17942750", "M0LLFmOuUVoF79m0dAbMXv5dqwWRWheu", "54.173.237.152", UNIX_TIMESTAMP())
File: /includes/database.class.php
Line: 98
Backtrace: