With all the IPSW firmware versions, various Apple devices and a variety of tools for jailbreaking the whole process becomes very confusing. While working with custom firmwares and jailbreaking one must follow the correct sequence of steps with right tools and software versions, otherwise iTunes throws an error and the device gets locked down in a restore or DFU loop.

One such often encountered error while restoring an custom IPSW file using iTunes is - "An unknown error occurred (Error 1600)." as shown below.

Apple blocks users from restoring older iOS firmware's, while this is a good security feature and a method to avoid OS fragmentation. This also prevents users from using jailbroken and carrier-unlockable software versions.

This practice makes iOS upgrade difficult for users relying on software unlock like ultrasn0w which is supported on older basebands only, If you are trying to upgrade an Apple device to an non-supported iOS version even when using TinyUmbrella - the iTunes restore process may throw up error 3194 and 1600 as shown below.

Here are solutions to get past these errors and flash custom, snowbreezed IPSW files to your Apple iPhone, iPad and iPod's.