We all know that Apple has seeded iOS 5 GM to developers. Well, you can also restore to iOS 5 GM without the need of a paid developer account. Gold Master versions are the prior versions of final releases and most of the times, doesn’t have any differences. If you are one of those people who are aware of the fact and tried upgrading to iOS 5 GM through iOS 5 Beta 9. But experienced ‘your device is not eligible for requested build’ error or something similar to it, we have the remedy for you.
All you need to do is to follow some simple steps to bypass this error. First of all find out the location of hosts file on your Mac/Pc. In Mac, go to Finder>Go to Folder, type ‘/etc’ and select go. Within few minutes, you would be in the /etc directory and look out for the file hosts. Copy it on desktop, manipulate and replace with the original one. If you are on Mac OS X Lion, follow the tutorial here. In Windows, the location is, C:WindowsSystem32driversetc.
Open the hosts file. In hosts file, remove the following lines if present ‘126.96.36.199 gs.apple.com. Once removed, save and revert back to iTunes. Now, try restoring your iDevice with shift+restore (PC) and option+restore (Mac). You won’t get the same error again and the restore will be successful.
Note that only Factory Unlocked users should restore to iOS 5 GM. Otherwise, you will lose the unlock forever. You can also JailBreak iOS 5 GM using Redsn0w, tethered though.