I'm not able to reproduce with the page you sent.
From what i see in the view, it only uses the vouchers table:
CREATE
DEFINER = 'root'@'127.0.0.1'
VIEW catalogues.view_coupons
AS
SELECT
`vouchers`.`VoucherID` AS `VoucherID`,
`vouchers`.`VoucherCode` AS `VoucherCode`,
`vouchers`.`Description` AS `Description`,
`vouchers`.`StartDate` AS `StartDate`,
`vouchers`.`EndDate` AS `EndDate`,
`vouchers`.`Discount` AS `Discount`,
`vouchers`.`VoucherTypeID` AS `VoucherTypeID`,
`vouchers`.`catalogueID` AS `catalogueID`,
`vouchers`.`catItemId` AS `catItemId`
FROM `vouchers`
WHERE (((TO_DAYS(CURDATE()) - TO_DAYS(`vouchers`.`StartDate`)) >= 0)
AND ((TO_DAYS(CURDATE()) - TO_DAYS(`vouchers`.`EndDate`)) <= 0));
I need more specifics on how to reproduce the error in order to troubleshoot.