I’ve had this problem that Xcode 4.5 would run my app fine in the simulator, but didn’t do so anymore on the device. Something about the “derived data folder was not found”. I checked, it was definitely there.

Then I found this post on Stackoverflow to show some suggestions: http://stackoverflow.com/questions/11456312/xcode-suddenly-stopped-running-project-on-hardware-could-not-launch-xxx-app

This solution worked for me – Thanks Dhilip: http://dhilipsiva.blogspot.in/2012/07/xcode-could-not-launch-app-no-such-file.html