3GS bb5.13.04 4.2.1 upgrade help

[kentonxo]

Hi there wise hackers. I need help. I am on 4.1. I downloaded snowbreeze 2.2 on windows. I cooked up iOS 4.2.1. I went into my updated iTunes did the shift to update to my already cooked firmware. It starts to go through the update process. The screen goes from the dfu mode to a screen with just the apple then an error21. It won't Continue. I used the new tiny umbrella to put in and out of update mode.
Someone please advise as to a couple of solutions to my problem.
Phone is working fine now on 4.1.
I have an old bootrom. Thanks

[zoolman88]

Do u have shsh for 4.2.1 I would use ireb is ur iTunes pointed at Cydia for shsh of the firmware

[cncrim]

Need Redsn0w to put the phone in special DFU mode for custom firmware.

[i.Annie]

Need Redsn0w to put the phone in special DFU mode for custom firmware.

+1. That's the solution!