I was using Xcode 6.0.1 till now and things were fine. Then I upgraded to Xcode 6.1 and tried running my application(which has a deployment target of 7.0) in iPhone 6 simula
Rebooting did not help me.
Installing/Reinstalling Simulators worked!!
Look under (XCode Preferences-> Downloads -> Components)
Just had this problem with Xcode 8 beta 5. I downloaded ios8 and 9 simulators, but was not able to run my app. I simply deleted derived data and rebooted my computer. It worked for me.
Rebooting my computer fixed this exact issue for me. Same error was thrown for both iOS7 and iOS8 simulators. I'm on OS X 10.10 and Xcode 6.1.
It is a Mac problem, not an Xcode problem.
Logout the user, shutdown, restart or just reboot Mac. Your Xcode simulator will go back to normal.
For anyone still facing this issue, this command worked for me:
sudo killall -9 com.apple.CoreSimulator.CoreSimulatorService
Maintain an accurate list of iOS simulators
When upgrading, you may drag around old simulators no longer available with your current version of Xcode. You can clean these by running this command in Terminal:
xcrun simctl delete unavailable
Quit Xcode first just for good measures. From the documentation:
Delete a device or all unavailable devices.