A short reminder, because I ran into this today and Xcode’s very poor at providing you useful verbosity when debugging Auto-Layout stuff done in Interface Builder. Sometimes (Xcode 4.x and 5.x) you might get the following errors when building an iOS project:
Auto Layout on iOS Versions prior to 6.0
Going to each error does not help much. Debugging IB auto-layout errors is still a painful process. You have to know in advance the root cause of such errors. Rant, Apple !