I have an app that worked fine in the released version of Xcode. I downloaded the beta and after I fixed all the little changes I ran it and it worked. I just came back and ran it again and I get an error saying
The request to open "com.matthewhsingleton.Smoke" failed . (null) was unable to service the request.
After reading @Droppy suggestion I read the thread and it is a common issue. To solve it is as follows
Problem solved for by an Apple Engineer in the lab. It's an issue they're working on. The bottom line was that when I copied Xcode to Applications folder, there was a bit set on it and that was preventing it from communicating with the simulator.
To fix it: Copy-paste Xcode-beta.app from Applications folder to somewhere else, e.g. Documents folder. Delete Xcode-beta.app from Applications folder. Move Xcode-beta.app from Documents to Applications folder again.