I get the same exact error
1064 - You have an error in your SQL syntax. Check the manual that corresponds to your MySQL server version for the right syntax to use near 'EXISTS(SELECT * FROM uhtml_newsletters_sent WHERE customers_id=
SELECT c.customers_id, c.customers_firstname, c.customers_lastname, c.customers_email_address FROM customers c WHERE customers_newsletter = '1' AND NOT EXISTS(SELECT * FROM uhtml_newsletters_sent WHERE customers_id=c.customers_id AND newsletters_id='3') LIMIT 10
Does anyone know how to fix this?