I\'m moving part of my projects to iOS 5 / ARC. One of the oldest project (iOS 4.2, armv6 for support iPod Touch 2g) is giving to me:
dyld`dyld_fatal_error:
If you go to the Console Output you'll se an error telling which framework is missing in the device and causing the problem (like grundyoso said in his answer).
So in order to fix this you can go to the target's General tab and add the missing framework in the Embedded Binaries section.
This will copy the framework to the app so it will never be missed on any device.