With Mountain Lion and the latest version of Xcode (4.4.4F250), none of the suggestions in this thread worked directly (clean, clean project, remove derived data folder, etc). This sequence did. From DhilipSiva:
- Disconnect your device
- Delete the app from your device
- Quit Xcode (Don’t just simply close the window, quit it)
- Delete derived data folder
rm -fr ~/Library/Developer/Xcode/DerivedData(console) - Start Xcode,connect device & run the project