Database Error!

Error: Field 'last_seen' doesn't have a default value
Query: INSERT INTO users (uid, password, ip_address, first_seen) VALUES ("5c9a9aa15c8d58.95280599", "9IMOzdfSGoCmLaGbKtdD00Y1Bc6o6saL", "54.242.115.55", UNIX_TIMESTAMP())
File: /includes/database.class.php
Line: 98
Backtrace: