Maximum Amount error message

I'm trying to stop/edit the error message that displays when the maximum product amount is reached on my store. This max amount is set to £1,500 in System > Config > Sales > Sales > Maximum Order Amount > Single Order Maximum Amount

When this amount is exceeded on the front-end of the website, the following (attached) error appears, instead of the error message defined in the config settings above - Any ideas?

http://www.purition.co.uk/shop-by-pr...ein-shake.html

Attachment 2216

Here's a couple of great extensions that can easily solve this problem for you:

http://inchoo.net/magento/magento-ma...-order-amount/

https://genmato.com/maximum-order-amount