This is what I ll do. Just it will take more than 15 days in order to get it back as they told me. I am a bit frustrated because I have received a brand new phone with a "defect" as it seems and they do not even want to replace it with a new one.

Because just flicking the apple logo and would not start. I plug it in my laptop and directly itunes opened and a message that restore and update is needed came up.

Hello everyone, I have exactly the same problem. I have been thru the guide, and i am sure I did everything correct, but still error 21. FYI I have a brand new Iphone 4s which have not even switched on for the first time. From the beginning its creating me the same problem.