-One of the site that was running ok suddenly had three duplicate orders.
-As is the case we analysed and didnt find any code related issues.In that space of time some admin pages were also not uploading css indicating something is wrong at server end.
What was happening ?
-When in Magento an order is placed using AIM authorize module.Curl connection is set up for 30 seconds.Here first the request is sent to Authorize.net payment gateway which internaly communicate with credit card gateways and as per the response responds back.
-This response is then handled by magento code.
-As there are few internal communication response from Authorize.net might be delayed by few seconds not if server is loaded and is slow curl might time out as the execution time will add up.
-We confirmed that it was something at server end.Initially the server guys were reluctant to accept but later informed that there was some server upgrade so for few hrs it was a bit slow.