Problem with PayPal

-- url of the page with the problem -- : salsashoes.com.au
-- HikaShop version -- : 2.3.0 Essential
-- Joomla version -- : 2.5.19

Hi,
I am having problems with PayPal processing payment. Sometimes when an order is processed by the user and trying to be automatically directed to PayPal, a message from PayPal stating that a problem has been encountered by the merchant (me) account. Also the message state that the order number has already been processed. I contacted PayPal and they seem to believe that nothing is wrong with our account (mind you payment to our account can be accepted through 4 different emails).
The problem appears intermittetly.
Any help is much appreciated.
Regards.

Hello,
Can you give us more information about the error message that you are having ? Also, note that checking that documentation will probably help you : www.hikashop.com/support/documentation/i...nt-paypal-error.html

Hi,
I read the suggested website and it seems the error I am getting is listed. I have followed the instructions so to enable multiple for the same invoice. (See original error attached).
I am hoping that this should resolve the problem.
Regards.