Baffled by error

[Mike Blezien]

Hello,

MySQL 4.1.12

trying to figure out why I keep getting this error with the following query:

SELECT c.account_id,a.name,a.company,SUM(c.agent_product_time) AS mins 
FROM account a LEFT JOIN calls c ON c.account_id = a.id 
WHERE c.calldate >= DATE_SUB(NOW(),INTERVAL 14 DAY) AND c.agent_id = 9
AND SUM(c.agent_product_time) >= '500' GROUP BY a.account_id
ORDER BY mins

ERROR: #1111 - Invalid use of group function 

Any help appreciated...

Mike(mickalo)Blezien
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