As soon as iOS 4 was released most of the people installed it and tried and some were experiencing the annoying 1604, 1600,3002 error codes when restoring to iOS 4 custom firmware in iTunes which was built using PwnageTool 4.0 or 4.01. but this issue does not happen to all only some users has reported this error in their iphone so from now they will be able to fix the problem using some easy process but note it that This is not a official solution but following the steps might fix the iTunes issue.
you will get the following 16014 and 1600 error appears :
The iPhone “[name]” could not be restored. An unknown error occurred.
16xx and 21 Error in iTunes during iPhone 3.1 Restore
so if you want to get rid of the problem, simply follow the below instructions:
1. You need not reinstall iTunes and keep the same version that you have used to restore or backup previously.
2. but Make sure that iPhone is disconnected from your computer and that iTunes is closed.
3. The following step of fixing 1604 iPhone restore error is Windows XP specific, if you are a Mac user, you may have to locate the folders yourselves as I am not sure: Go to folder C:\Documents and Settings\\Application Data\Apple Computer\iTunes\iPhone Software Updates. You will see one or more files. Cut and paste them somewhere else. Do not delete them in case the steps does not work for you, you can still copy them back to the folder. You can find out your username by doing a Ctrl-Alt-Del. If somehow you cannot find the folder, you are probably in the wrong user directory.
4. so Launch iTunes and put your iPhone in recovery mode. Refer to this article on Unable To Restore iPhone on how to do put iPhone in recovery mode.
5. Now proceed with restore and iTunes will download the update online. If you are downgrading to a lower version, do step 3 and leaving only the firmware file that you want to downgrade to. Double click on the file and iTunes will begin the restore.
And its all done..
Do let us know if this worked for you. [via]