That is really annoying. This error happens in a number of different situations. Sometimes restarting the Xcode, fixes the problem. If not, follow these steps:
Disconnect your device.
Delete the app from your device.
Quit Xcode (Do not just simply close the window, quit it)
Delete derived data folder (~/Library/Developer/Xcode/DerivedData/-gbrvhlvwmpiobxdujegtghggrffp - or something like that)
Now start Xcode once again, connect device and run the project. It should work fine.
from DhilipSiva blog
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…