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

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