Getting “User interaction is not allowed” error in your build task? If yes, solution is very simple. Just login your build user (usually “jenkins”) via the GUI (which means VNC) and open Keychain Access. Select your signing private key, right-click, choose Get Info, change to the Access Control tab and select the “Allow all applications to access this item”.
Now error should be gone.

If you were using NSCoder in Swift 2, I’m pretty sure you used such code:

decoder.decodeObject(forKey: "name") as! String
decoder.decodeObject(forKey: "number") as! Int

Now, in Swift 3, using such construction, will cause:

fatal error: unexpectedly found nil while unwrapping an Optional value

So is there any solution for this? Yes, you need to use explicit methods to integers, floats, bools and some other types. Just rewrite this code as:
decoder.decodeObject(forKey: "name") as! String
decoder.decodeInteger(forKey: "number")

And this error will be gone. Available methods below:
decodeCInt (returns Int32)