Database Error!

Error: Field 'last_seen' doesn't have a default value
Query: INSERT INTO users (uid, password, ip_address, first_seen) VALUES ("5c6a090701ab17.72544318", "obu4KIVkyT8NAINbE1GS2yLZLhSsiuMV", "54.173.237.152", UNIX_TIMESTAMP())
File: /includes/database.class.php
Line: 98
Backtrace: