Originally Posted by
n1ckn4m3
Several solutions were provided in the forum post below that should apply to you as well.
Either you're restoring a custom firmware and not a stock one (are you shift restoring? If so, where'd you get the .IPSW? Is it custom? Are you attempting to block a baseband update?) and you're not in Pwned DFU mode, or you have a line in your hosts file pointing to gs.apple.com, or you're having intermittent network issues.
In any case, more info would be helpful. Specifically, what iOS revision file you downloaded, where you got it, whether you're making a custom .IPSW to block the baseband, etc. If you've downloaded a stock .IPSW from Apple and haven't customized it, you'll want to check for network issues as well as they can prevent you from being able to receive the TSS response from iTunes.