Unable to determine simulator device to boot. - Xcode

Question

I just downloaded Xcode 6 & played with it a bit.

After switching back to previous version of Xcode and running in simulator, I keep getting this error.

Answer 1

In my case I had such a message just because the simulated device was still booting (longer than usually, I guess). Xcode 7.2. (This is not actually an answer to this specific question, but I came here googling the message in the title, so I am writing my note here for if someone else gets the same case as I did)

Answer 2

You will not see the profiles of simulator without a rebooting of OS X.I added simulator for many times,when the rebooting finished, it shows on the device list under the simulator bar. I think this is a bug of Xcode 6 Beta

Answer 3

I had the same problem when running from Xcode 6 beta selecting iPhone 5s. If I choose iPhone 5 or "resizable iPhone" then my app launches fine.