Symptom
UPDATE `users` SET `login_date`='2006-05-16 15:52:42' WHERE UNIX_TIMESTAMP(DATE_SUB('2006-05-16 15:52:42', INTERVAL 1400 SECOND)) > UNIX_TIMESTAMP(last_request_time) AND (`login_date` ='0000-00-00 00:00:00')User '1081195576' has exceeded the 'max_questions' resource (current value: 18000)
User 'username' has exceeded the 'max_questions' resource (current value: 18000)
Solution
Your hosting service sets a limit of 18000 queries per hour. If you exceed this limit in an hour, then the above error will be shown.
Upgrade your hosting to a package with more resources.