How to Fix iTunes Error 1600 While Restoring iOS 5 Beta Custom IPSW?

Hello Nickson, iTunes “Error 16xx” occurs when you are trying to restore a custom firmware without pwning the iBoot of your iOS device. And in your case, iTunes gives error 1600 because you restored a custom iOS 5 beta 2 firmware using the regular DFU mode. So every time you restore a custom firmware, which is not allowed by Apple, your iOS device will send a message to iTunes to not to restore it. In order to configure this error, you will need to put your iOS device into Pwned DFU Mode using iREB. You can follow the step by step guide posted below to fix iTunes error 16xx using iREB RC4 for Windows. Mac users can use Redsn0w as iREB’s alternative.

Step 1: First, download iREB RC4, extract it, and save it on your desktop.
Step 2: Connect your iPhone 4 into your PC via USB cable and launch the downloaded launch iREB-r4.exe.
Step 3: Then put your iOS device in DFU mode by pressing the Power and Home button at the same time for 10 seconds and then release the Power after 10 seconds but continue holding the Home button. If everything goes accordingly, iREB will prompt you that your iOS device is in DFU Mode.
Step 4: iREB will soon start injecting the Limera1n exploit in the iBoot.
Step 5: Once completed, iREB will inform you that your iPhone is in Pwned DFU mode.
Step 6: Then wait for at least 10 seconds or so and launch iTunes and restore from there.
Step 7:  Once iTunes is opened, select your device at the left side panel and. Make sure that you are pressing SHIFT while clicking on the Restore button and browse for the iOS 5 beta IPSW and hit OK to commence the restoration process. If you have encountered error 16xx again, immediately untether your iPhone perform the entire process.

You can check this blog post for detailed tutorial and screenshots.