How to Fix iTunes Error 1004 on iPhone 4 restoration !! [Guide]

More complete solution for those not knowing where to find the file:

On Mac:

•   Open Finder
•   Hold down COMMAND + SHIFT keys and press 'G'
•   Enter "/private/etc/" in the field and press "Go"
•   Find "hosts" file in the directory
•   Drag the file to your desktop
•   Open it in text editor
•   Remove the line that has gs.apple.com entirely or put a # at the beginning of it to comment it out
•   Save the file
•   Drag it back to the /private/etc/ folder.
•   You'd need to enter your username and password to authenticate the move

On Windows:

• Locate the hosts file in one of the following directories:
• Windows 95/98/Me c:\windows\hosts
• Windows NT/2000/XP Pro c:\winnt\system32\drivers\etc\hosts
• Windows XP, Vista, 7 c:\windows\system32\drivers\etc\hosts
• Right click and click on "Open With..." and then click on "Notepad" on the list.
• Remove the line that has gs.apple.com completely and save the file.
• This should work fine.