If you hit a 1604, 1603, 1602, 1601, 1600 error while trying to restore your iPhone with a custom iOS 4.2.1 firmware file created using Sn0wbreeze 2.2 for Windows or PwnageTool 4.2 for Mac then there is a way to bypass the error.
iH8sn0w, developer of Sn0wbreeze has released a new version of iREB tool, which is compatible with iOS 4.2.1.





