Found this hope it helps..........
How to go about fixing 1604 iPhone restore error? Thousands of iPhone users are plagued with this issue. You may have also come across many articles asking you to do this and that but ended up with the same error. Well, I cannot guarantee that what is written here will help you in your quest to fixing 1604 iPhone restore error so do it at your own risk.
Steps to fixing 1604 iPhone restore error:
1. There is no need to reinstall iTunes or whatever. Keep the same version that you have used to restore or backup previously.
2. 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\<username you use to login to windows>\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. 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. 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.
Kindly note that restoring iPhone clears ALL personal data. In this case you probably have no choice due to the error. I hope this article has been of help to those in the mist of fixing 1604 iPhone restore error. Again, this make not work for all.
