Does anyone know of a way to fix this? I am trying to update/restore my iPhone and it keeps giving me an error 21 which I looked on apple's website and says its a security system issue or something along those lines? If you can help me, that would be very appreciated!

I am currently running 4.3.1 (I've heard apple stopped signing this?)
because I just never really updated to 4.3.2 so I hope thats not the issue.
iPhone for AT&T. hmm if you need any more info to help me, request it and I will gladly be willing to give it unless its personal. Thanks!