Check the schemes menu at the top of the Xcode project window. Look at the destination you're trying to run in. If you run in the simulator, you don't need to sign your project.
If you run in a device, you need to attach the actual device. It must not say "generic device".
~ Answered on 2016-09-20 21:14:21
In my case this error disappeared when I changed the "Bundle Identifier" to something less generic (e.g. adding some random numbers at the end)
~ Answered on 2017-04-28 19:52:03