It seems that the payment request sent from authorize.net to HikaShop with the payment information in the POST is being redirected to another URL without the POST information when MobileJoomla is activated.
Thus, when it reaches the payment notification processing in HikaShop, the payment information is nowhere to be found and the order cannot be validated.
The notification URL is not SEFed and looks like that:
http://example.com/index.php?option=com_hikashop&ctrl=checkout&task=notify¬if_payment=authorize&tmpl=component&lang=en&Itemid=18
Would you have any idea of why this would happen ?