i am having same problem, here is what i have found, testing right now.
Delete the iOS 6 IPSW as you won't be able to use it again.
Uninstall iTunes 11.1 and all of its cache (make sure you remove the cache). Restart your PC if prompted to. Then reinstall a copy of iTunes 11.0.5 from the direct links below. If you have any libraries or locally cached data that you want to keep, temporarily store them somewhere until you get the situation fixed
Mac OSX:
https://secure-appldnld.apple.com/iT...unes11.0.5.dmg
Windows 32 Bit:
https://secure-appldnld.apple.com/iT...TunesSetup.exe
Windows 64 Bit:
https://secure-appldnld.apple.com/iT...nes64Setup.exe
Thanks to willerz2