XCode8 iMessage Swift 2.3 dyld: Symbol not found: __swift_getInitializedObjCClass ,Message.appex/../../Frameworks/libswiftCore.dylib

dyld: Symbol not found: __swift_getInitializedObjCClass
Referenced from: derived_path/PlugIns/Message.appex/Message
Expected In: derived_path/PlugIns/Message.appex/../../Frameworks/libswiftCore.dylib
in derived_path/PlugIns/Message.appex/Message

This problem occurs because of the difference of the target swift versions . You need to set swift version same in the both of the main target and imessage extension target.

Related apple developer forum post : https://forums.developer.apple.com/thread/48740