With iOS 8, Apple changed the location your apps save/load their files to/from. As such, we have had to adjust to this new scheme. Our saving/loading now supports iOS 8 as well as iOS 7 and older, but you will need to rebuild and resubmit apps if you wish them to work on iOS 8. All new app submissions to the AppStore must be built with at least 1.3.1443 or 1.4.1451 also, as you must have iOS 8 support otherwise your app will fail submission.
You will need to update to Xcode 6 in order to make applications (6.1.1+ in recent versions of Studio or if you want to use YYC).
Please be aware also that Apple have made their iDevices require you to enable the use of them in developer mode - otherwise, Instruments will throw a build "error" when deploying your game to your iDevice and GameCenter won't even attempt to connect. Please note that in releases starting with EA314 and 1.4.1500+ Instruments has stopped being used in favour of new tools in Xcode 6.1+.
For Instruments: Settings > Developer > Enable UI Automation must be ON.
For GameCenter: Settings > GameCenter > Sandbox must be ON.
The Instruments error is the same as it often did with Xcode 5.x anyway, although the wording has changed slightly. Please note that with Xcode 6 you will almost always get a build "failed" warning when using iOS7 and older devices now, as Instruments isn't intended for those OS versions now. Your build has NOT failed, it just couldn't be launched automatically by Instruments and so it reported an error code to GM. If you see any Instruments error your build was fine and the app installed okay on your device, it's just waiting for you to launch it manually.