As mentioned in the Xcode 6.1 Release Notes, the issue is that you are linking against new frameworks that were added to both Yosemite and iOS 8 while running in iOS 7.1. Unfortunately, this causes dyld to try bringing in the host version of the library when running in the iOS 7.1 simulator runtime.
If an app is weak linked against frameworks new in iOS 8 SDK and OS X
10.10 SDK, it may fail to run if the run destination is an iOS Simulator for older iOS runtimes and the host system is running OS X
Yosemite. (17807439)
Additionally, this can occur if your iOS 7.1 simulator runtime is not fully installed (eg: due to an interrupted installation). If this occurs, dyld will similarly fall back to the host for the missing libraries if available.
iOS 8.0 and later have their own dyld that will reject pulling in host versions of libraries and thus will prevent this class of problems in the future.
The iOS 7.1 Simulator runtime that is installed by Xcode 6.2 and later was updated to address this issue.
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