App installation failed: Unknown Error Xcode 7

Question

My app runs fine in the simulator, but when I try to install it on my iPhone it says

App installation failed: An unknown error has occurred.

Answer 1

This line in the device logs stood out to me, and hopefully you saw it too:

Failed to verify code signature of /private/var/mobile/Library/Caches/com.apple.mobile.installd.staging/temp.FvOJz0/extracted/FSS App.app/PlugIns/QuickSched.appex

This is saying that (although Xcode thought everything was OK at build time), your device rejected the code signature of your app extension.

There are a few solutions here, but in my personal experience, this issue can only be fixed by tinkering with the code signing settings for your app and app extension. Make sure that the app and app extension are being signed with the same certificate (although likely different provisioning profiles).

As others have recommended, I've also been able to fix this by running the Clean action in Xcode for the project, and also by deleting the derived data directories. But I have not always been successful with this.