I was on ElCaptian with an Xcode 8 ( and also had Xcode 7 version). I updated to Seirra & Xcode 8.2.1 and also deleted Xcode 7, yet keep getting this error whenever I run my project.
The Simulator runs the app fine, only that Xcode is no longer linked to the simulator and I can't do any debugging.
I was told I need to delete previous Simulators. I went to /Library/Developer/CoreSimulator/Profiles/Runtimes and deleted iOS 9.3.simruntime. Yet I still get the error. I clear my Xcode with Cmmd + K, also I do Cmmd + Shift + Option + K. I also attempted to reset Content and Settings of my Simultator, but non have worked.
The only solution that has worked for me is restting my Macbook, which is inconvenient.