Sync result showing empty response

Hi,

I've and application that is using the BULK API to upsert contacts as well as data cards into Eloqua. For that purpose, our app creates a custom import definition, submits data to it and gets the sync URL for later fetching of the results of the sync.

So far in the tests we have done, it was working ok. But in recent runs, it was working only 1 of 3 times it tried. Everyone of them where different import definition (different in identity, but with the same structure) and we got different sync numbers.

The problematic ones are answering something like:

/sync/4863/results

{
  "elements":
  [
  ],
  "total":0,
  "pageSize":1000,
  "page":1
}

While the ones with success (success in the request, not the process) are answering

{

  "elements":

  [

   {

    "syncUri":"/sync/4861",

    "count":0,

    "severity":"information",

    "message":"Successfully converted file 2013-03-14T17-00-38_User398_d8799f5059194804aa33536cf68ec2e5.csv.NOW18_pid6968.original to 2013-03-14T17-00-38_User398_d8799f5059194804aa33536cf68ec2e5.csv.NOW18_pid6968.staging",

    "createdAt":"/Date(1363280440210)/"

   },

   {

    "syncUri":"/sync/4861",

    "count":0,

    "severity":"information",

    "message":"File 2013-03-14T17-00-38_User398_d8799f5059194804aa33536cf68ec2e5.csv.NOW18_pid6968.staging processed and deleted.",

    "createdAt":"/Date(1363280447807)/"

   },

   {

    "syncUri":"/sync/4861",

    "count":3,

    "severity":"warning",

    "message":"Total rejected records.",

    "createdAt":"/Date(1363280588843)/"

   },

   {

    "syncUri":"/sync/4861",

    "count":0,

    "severity":"information",

    "message":"CustomObject data created.",

    "createdAt":"/Date(1363280588843)/"

   },

   {

    "syncUri":"/sync/4861",

    "count":3,

    "severity":"information",

    "message":"CustomObject data updated.",

    "createdAt":"/Date(1363280588843)/"

   }

  ],

  "total":5,

  "pageSize":1000,

  "page":1

}

The first answer, the empty one we are getting now, represents a problem since we can't get information from it. Besides in this case, nothing was imported into Eloqua and there is no way for us to know what happened.

Any clue on what could be happening? How can I prevent that to happend? I can provide more info like import definition if necessary.

Thanks in advance.