Unable to determine simulator device to boot. - Xcode

ios, ios8, xcode, xcode6

Solution

Make sure you have only one iOS Simulator instance running in the Dock.

Problem

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. Unable to determine simulator device to boot. How do we resolve this? Thanks in advance.

Original source