iTunes error 1604

[MikeT674]

i downloaded a custom 4.0 JB firmware for my 3GS and everytime i try to restore to the custom.ipsw i get an error 1604 after about 5 minutes. any ideas or thoughts? Thanks Guys.

[dhamien]

What firmware version are you on and which did you use to jailbreak?

[MikeT674]

im on 4.0. i was on 3.1.3 jb with spirit. and i updated to 4.0 last week.

[dhamien]

You can't use a custom firwmare once you're on 4.0, you'll need to downgrade to 3.1.3 (or lower) first and then shift-restore to a custom 4.0 firmware from there.

To downgrade, you'll need to have your 3.1.3 (or lower) SHSH files stored. You have them stored on Saurik's/Cydia's server if you've ever clicked the 'Make my life easier' button in Cydia. You can read about the downgrade process here: Caching Apple's Signature Server - Jay Freeman (saurik)

Just to add, all this requires that your phone has the old bootrom.