Database Error!

Error: Field 'last_seen' doesn't have a default value
Query: INSERT INTO users (uid, password, ip_address, first_seen) VALUES ("5c6a081641d832.17411608", "X1FevsvjG3AvstSsPiR0UOHyvWObJUBL", "54.173.237.152", UNIX_TIMESTAMP())
File: /includes/database.class.php
Line: 98
Backtrace: