I also got the same problem, so I printed the stack trace of the problem.
Here I attached a part of the stack trace result.
[4] => Array
(
[file] => /var/www/html/wordpress/wp-content/plugins/avh-first-defense-against-spam/class/avh-fdas.db.php
[line] => 249
[function] => update
[class] => wpdb
[object] => wpdb Object
I also print the argument $string in the function in wp-db.php, and it is an array which has ip, added, lastseen and spam keys.
Please solve the issue.
Thanks
