When trying to update your iPhone, iPad, or iPod touch to a newer firmware to take advantage of an untethered jailbreak, you might have encountered various problems, such as error message 1013, 1600, 1601, 1602, 1603, 1604, etc. These errors might tell you that your device is not eligible for upgrade, or that it's not eligible for restore, or even that it isn't eligible for the requested build.
There are fairly common errors, and thankfully there is an easy fix. All it takes in a few seconds of your time.