Persistent 1604 error when trying to upgrade via iTunes

[Krupke]

I am simply trying to upgrade my iPhone 4s with Apple's latest firmware, using recovery mode (not DFU, though I tried that). Nothing's working. It goes through the motions, but I keep getting error 1604 (sometimes 1601) at the end of the process. I disabled virus and firewall during the process. I'm using the very latest iTunes (10.6.1.7), recently installed. I went and bought a high quality connection cable (plugging directly in the main USB port), in case it was my default cable. This is not a jailbroken phone. It is locked however, with a passcode I don't have. Could that be preventing a firmware upgrade or restore, or is there something I'm overlooking that may resolve the issue?