In recent days we've offered advice that if you plan to revert from iOS 8 to iOS 7, you do so in a hurry as Apple stops authorizing earlier versions of iOS days after it releases a major update. If you didn't follow that advice, you're too late.
As of Saturday, the steps necessary to revert your iPhone, iPad, or iPod touch no longer work. Instead of iTunes restoring your device, you see a message like the one above--your device can not be restored because it's not eligible for the requested build. This is iTunes way of telling you that Apple has closed the door and is no longer signing any version of iOS 7.
Unless your device was jailbroken prior to installing iOS 8 (some jailbreak schemes allow a path back) you are now committed to the latest version of Apple's mobile operating system.