Here is a quick guide for those iPhone, iPod Touch and iPad users who are getting iTunes error 3194, 21 or 1015 while restoring stock or custom IPSW of iOS 4.3.3. Error 3194 means iTunes failed to get iOS 4.3.3 SHSH blobs from Apple servers and error 21 means you are trying to restore the custom IPSW from recovery mode instead of DFU or Pwned DFU mode. Error 1015 means restore has been done but your iPhone is stuck in recovery mode loop.

Fix iTunes Error 3194:

Method 1 (Windows & Mac)

Connect your iDevice to your PC or Mac and launch TinyUmbrella (Windows | Mac). Go to Advanced tab and uncheck Request SHSH From Cydia option. Hit Apply Changes button and reboot your computer.

Method 2 (On Windows)

Navigate to C:\Windows\System32\drivers\etc and open HOSTS file with Notepad. Remove or comment all entries which contain gs.apple.com and reboot your PC.

Method 2 (On Mac)

Click Go -> Go to Folder and then enter path /etc
Remove or comment all entries which contain gs.apple.com and reboot your computer.

Fix iTunes Error 16xx (1600, 1601, 1602, 1603, 1604) & 21:

If you are restoring to iOS 4.3.3 stock IPSW, you need to put your iPhone into DFU mode by using the following instructions:

1. Turn OFF your iDevice completely
2. Press Home+Power button for 10 seconds.
3. After 10 seconds, release the Power button but keep holding the Home button until iTunes detect your iPhone into DFU mode.
4. Hold down the SHIFT key (ALT for Mac) and click on the Restore button in iTunes.
5. Select iOS 4.3.3 stock IPSW and leave the rest on iTunes. Once your iDevice has been restored, it will restart automatically

If you are restoring iOS 4.3.3 custom IPSW, you need to put your iPhone into Pwned DFU mode by using the following instructions:

1. Download iREB for Windows from here. Mac OS X users should follow this guide.
2. Launch iREB and select your iDevice name from the displayed options. Now put your iDevice into DFU mode by using the following instructions:
• Turn OFF your iDevice completely
• Press Home+Power button for 10 seconds.
• After 10 seconds, release the Power button but keep holding the Home button until iREB detect your iPhone into DFU mode.
3. As soon as iREB will detect your iDevice into DFU mode, it will patch the iBoot of your iDevice with Limera1n exploit and will put it into Pwned DFU mode.
4. Once done, your iDevice screen will be completely black. Launch iTunes and restore iOS 4.3.3 custom IPSW by using SHIFT+Restore combo on Windows and ALT(Option)+Restore combo on Mac OS X.

Fix iTunes Error 1013, 1014 & 1015:

Download TinyUmbrella (Fix Recovery) for iOS 4.3.x (Win | Mac). Download Zlib1.dll from here and place it in the same directory in which fixrecovery43.exe is present. Start iTunes in background and launch fixrecovery43.exe. Now use the following instructions to put your iPhone into DFU mode:

• Turn OFF your iDevice completely
• Press Home+Power button for 10 seconds.
• After 10 seconds, release the Power button but keep holding the Home button until fixrecovery43.exe detect your iPhone into DFU mode.

As soon as fixrecovery43.exe will detect your iDevice in DFU mode, it will use GreenPois0n exploit to kick your iDevice out of recovery mode loop. Once you see Exiting libpois0n text on your command prompt, rest of the process will be shown on your iDevice's screen. If you are still unable to kick your iDevice out of recovery mode, you can give Recboot, TinyUmbrella or EasyiRecovery a try.