$.postJOSN=function(destUrl, postdata, userCallback )
{  
    $.ajax({type:"POST",contentType:"application/json; charset=utf-8",url:destUrl,data:$.toJSON(postdata),success:SuccessCallBack,error:ErrorCallBack});
    
    function SuccessCallBack(result)
    {
        userCallback($.parseJSON(result));
    }
    
    function ErrorCallBack(Request,ErrorType,ErrorObj)
    {
        var errorObj=$.parseJSON(Request.responseText);
        var msg=errorObj.ExceptionType+"  "+errorObj.Message+ "\r\n";        
        msg += errorObj.StackTrace;
        alert(msg);
    }
}