jQuery ajax callback issue

jQuery ajax callback issue

When sending ajax request to my JSON Service method, the method inserts the data into backend and runs return true/false. Sometimes the success callback function is not being called after returning from JSON Service method without exception. I am unable to reproduce this in my development and qa environments. But it is happening to 1 or 2 users for every 1000 users in Production. If that users retry, it works with no issues.

Below is how I am sending ajax request

$.ajax(
{
   type: "POST",
   url: jsonSvcUrl + "/SaveItems",
   dataType: "json",
   data: JSON.stringify(data),
   async: false,
   contentType: "application/json; charset=utf-8",
   success: SaveSuccess,
   error: SaveFailed
});

I am using jQuery 1.4.2. Is there a solution for this issue.