I've NEVER jailbroken my phone/ipad 2 and I'm getting the same message/error.
I just turned off the Firewall to see if that let's me update.
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Yeah, it won't let me update my iPhone 4 or my iPad 2.
I disabled the Firewall on my MBP and tried using the direct downloaded file I got from the top of the forum and the one using the built in update/restore in iTunes, neither are letting me update.