Today I got the memo from Apple as probably every other Apple developer about potentially infected Xcode installations. (https://developer.apple.com/news/?id=09222015a)
I was getting the same message "a sealed resource is missing or invalid". However i was able to rectify the issue by going into the App Store and downloading the latest version of Xcode - Version 7.0 (7A220), and this seems to have rectified the issue.
Although i did first try updating Xcode through the updates section on the App Store, but for some reason this didn't work. So i would recommend going into the App Store > Search for Xcode > Then install the latest version available to you.
The false positive validation issue appears to be caused by containing previous iOS SDKs in order to be backwards compatible.
A clean install will completely wipe the SDK directories. When you run the validation test after a clean install it will pass. Once you copy previous iOS versions, which, for us, is iOS 8 for iPhone, the validation will fail.
This scenario was tested after updating to XCode 7.0.1 (7A1001) which was released earlier this afternoon.
In order to avoid a clean install, you can temporarily remove the previous SDK version from their respective location, and run the validation. Then, once the validation passes, copy the files back where they belong.
Depending upon gatekeeper settings.please check gatekeeper settings to allow anywhere and revalidate Xcode.