Unable to boot device in current state : Creating

This problem happened to me when I renamed Xcode app from 'Xcode 2.app' to 'Xcode6.app' (I have both 5 & 6 Xcodes installed)

This answer helped me: https://stackoverflow.com/a/26151149/2764408

You will need to delete this device from your simulator and recreate it.

From inside the iOS Simulator application menu, choose Hardware > Device > Manage Devices

In the Simulators list on the left, select the device that is unable to boot and press the delete key

Now use the + in the bottom left to add a new device with the same hardware / OS configuration.

This is mentioned in the Xcode 6.1 Release Notes

Simulated devices can get stuck in a “Creating” state in some circumstances. This problem can occur either when creating new devices or when resetting existing devices after having renamed Xcode.app.
If this this problem occurs, reboot your system and reset the device from the command line by running xcrun simctl erase <Device UDID>. You can obtain the UDID of the device by checking the output of xcrun simctl list.