[Dave]

@Scimia
I fixed that error for someone not too long ago.
Open the file /mailchimp/MailChimpSubs.php

Around line 127 you have:

$qry = "INSERT INTO " . TABLE_PREFIX . "kws_mailchimp_log values(NULL,now(),'C',NULL,'".serialize($this->errors_arr)."')";

Replace with:

$qry = "INSERT INTO " . TABLE_PREFIX . "kws_mailchimp_log values(NULL,now(),'C',NULL,'".$vbulletin->db->escape_string(serialize($this->errors_arr))."')";