I have been jailbreaking/unlocking since the original iphone came out and this is the first time I have had an issue. I really could use someone's help cause I just sold my phone on ebay and I need to ship it to the guy soon. This all started when I was resetting my phone settings and deleting my personal info on the phone. Its a 3GS with the newer bootroom. I was at 4.2.1 cooked with pwnage and tethered jailbroken with redsn0w and unlocked with ultrasn0w at baseband 5.12.01. Everything worked fine till i was getting ready to ship it and reset all settings and wiped the phone. after the reboot i was stuck at the apple logo. So I went into DFU mode and tried to restore with a custom 4.2.1 firmware. It would fail. I would get error 1600. I read somewhere that starting with 4.2.1 that once you put it on and jailbreak it, you can't put it on again. I am not sure if its true. Anyways, I tried restoring in recovery mode and no luck. I tried rejailbreaking it with redsn0w but it would stall at "installing bundles". So I tried downgrading to and standard 3.1.2 firmware and it worked. from there I once made back to a custom 4.2.1 but when I tried to jailbreak with greenpois0n, it crashed my and my phone was back in recovery loop and I couldn't restore again to 4.2.1. I was able to go back down to 3.2.1 tho. so that is where i am at now and every time i try to restore with a cooked 4.1. or 4.2.1 firmware, i get a error 21 in itunes and I need to use tinyumbrella to kick it out of recovery mode afterwards.
Does anyone have any idea what happened and how can I get this phone back to 4.2.1 without upgrading the baseband so I can eventually unlock and jailbreak the phone again? I really could use someones help here. Im pretty experienced so quick solutions are fine. I can't afford to refund the money to the buyer either. Thanks to anyone whiling help. Seriously.