iPhone developer iH8sn0w has just released a new version of iREB which is compatible with all iOS 4.2.1 devices. You can use it to bypass 1604, 1603, 1602, 1601, 1600 error in iTunes during custom iOS 4.2.1 firmware restore which has been created using either Sn0wbreeze or PwnageTool.

When trying to restore your iPhone or iPod touch in iTunes with iPhone 3.1 firmware, you may get an error message followed by an error code 1601, 1602, 16xx or 21. To get around this problem, iH8Sn0w has released a handy little tool called iREB (iTunes Restore Error Bypasser) for both Windows and Macs which can help bring your iPhone back to life. The latest version of this program supports iPhone 3.1 firmware running on the original iPhone, iPhone 3G and iPod touch 1G.